diff --git a/lib/ansible/utils/collection_loader/__init__.py b/lib/ansible/utils/collection_loader/__init__.py
index a81f503966a..b63c239d20e 100644
--- a/lib/ansible/utils/collection_loader/__init__.py
+++ b/lib/ansible/utils/collection_loader/__init__.py
@@ -1,6 +1,14 @@
 # (c) 2019 Ansible Project
 # GNU General Public License v3.0+ (see COPYING or https://www.gnu.org/licenses/gpl-3.0.txt)
 
+# CAUTION: There are two implementations of the collection loader.
+#          They must be kept functionally identical, although their implementations may differ.
+#
+# 1) The controller implementation resides in the "lib/ansible/utils/collection_loader/" directory.
+#    It must function on all Python versions supported on the controller.
+# 2) The ansible-test implementation resides in the "test/lib/ansible_test/_data/legacy_collection_loader/" directory.
+#    It must function on all Python versions supported on managed hosts which are not supported by the controller.
+
 from __future__ import (absolute_import, division, print_function)
 __metaclass__ = type
 
diff --git a/lib/ansible/utils/collection_loader/_collection_config.py b/lib/ansible/utils/collection_loader/_collection_config.py
index 096797f0b7f..c0680942b4f 100644
--- a/lib/ansible/utils/collection_loader/_collection_config.py
+++ b/lib/ansible/utils/collection_loader/_collection_config.py
@@ -1,6 +1,14 @@
 # (c) 2019 Ansible Project
 # GNU General Public License v3.0+ (see COPYING or https://www.gnu.org/licenses/gpl-3.0.txt)
 
+# CAUTION: There are two implementations of the collection loader.
+#          They must be kept functionally identical, although their implementations may differ.
+#
+# 1) The controller implementation resides in the "lib/ansible/utils/collection_loader/" directory.
+#    It must function on all Python versions supported on the controller.
+# 2) The ansible-test implementation resides in the "test/lib/ansible_test/_data/legacy_collection_loader/" directory.
+#    It must function on all Python versions supported on managed hosts which are not supported by the controller.
+
 from __future__ import (absolute_import, division, print_function)
 __metaclass__ = type
 
diff --git a/lib/ansible/utils/collection_loader/_collection_finder.py b/lib/ansible/utils/collection_loader/_collection_finder.py
index e0c3c109b9e..2ac88ca3260 100644
--- a/lib/ansible/utils/collection_loader/_collection_finder.py
+++ b/lib/ansible/utils/collection_loader/_collection_finder.py
@@ -1,6 +1,14 @@
 # (c) 2019 Ansible Project
 # GNU General Public License v3.0+ (see COPYING or https://www.gnu.org/licenses/gpl-3.0.txt)
 
+# CAUTION: There are two implementations of the collection loader.
+#          They must be kept functionally identical, although their implementations may differ.
+#
+# 1) The controller implementation resides in the "lib/ansible/utils/collection_loader/" directory.
+#    It must function on all Python versions supported on the controller.
+# 2) The ansible-test implementation resides in the "test/lib/ansible_test/_data/legacy_collection_loader/" directory.
+#    It must function on all Python versions supported on managed hosts which are not supported by the controller.
+
 from __future__ import (absolute_import, division, print_function)
 __metaclass__ = type
 
diff --git a/lib/ansible/utils/collection_loader/_collection_meta.py b/lib/ansible/utils/collection_loader/_collection_meta.py
index b14917c30e2..756cd7ac6ea 100644
--- a/lib/ansible/utils/collection_loader/_collection_meta.py
+++ b/lib/ansible/utils/collection_loader/_collection_meta.py
@@ -1,6 +1,14 @@
 # (c) 2019 Ansible Project
 # GNU General Public License v3.0+ (see COPYING or https://www.gnu.org/licenses/gpl-3.0.txt)
 
+# CAUTION: There are two implementations of the collection loader.
+#          They must be kept functionally identical, although their implementations may differ.
+#
+# 1) The controller implementation resides in the "lib/ansible/utils/collection_loader/" directory.
+#    It must function on all Python versions supported on the controller.
+# 2) The ansible-test implementation resides in the "test/lib/ansible_test/_data/legacy_collection_loader/" directory.
+#    It must function on all Python versions supported on managed hosts which are not supported by the controller.
+
 from __future__ import (absolute_import, division, print_function)
 __metaclass__ = type
 
diff --git a/test/lib/ansible_test/_data/legacy_collection_loader/__init__.py b/test/lib/ansible_test/_data/legacy_collection_loader/__init__.py
index a81f503966a..b63c239d20e 100644
--- a/test/lib/ansible_test/_data/legacy_collection_loader/__init__.py
+++ b/test/lib/ansible_test/_data/legacy_collection_loader/__init__.py
@@ -1,6 +1,14 @@
 # (c) 2019 Ansible Project
 # GNU General Public License v3.0+ (see COPYING or https://www.gnu.org/licenses/gpl-3.0.txt)
 
+# CAUTION: There are two implementations of the collection loader.
+#          They must be kept functionally identical, although their implementations may differ.
+#
+# 1) The controller implementation resides in the "lib/ansible/utils/collection_loader/" directory.
+#    It must function on all Python versions supported on the controller.
+# 2) The ansible-test implementation resides in the "test/lib/ansible_test/_data/legacy_collection_loader/" directory.
+#    It must function on all Python versions supported on managed hosts which are not supported by the controller.
+
 from __future__ import (absolute_import, division, print_function)
 __metaclass__ = type
 
diff --git a/test/lib/ansible_test/_data/legacy_collection_loader/_collection_config.py b/test/lib/ansible_test/_data/legacy_collection_loader/_collection_config.py
index 096797f0b7f..c0680942b4f 100644
--- a/test/lib/ansible_test/_data/legacy_collection_loader/_collection_config.py
+++ b/test/lib/ansible_test/_data/legacy_collection_loader/_collection_config.py
@@ -1,6 +1,14 @@
 # (c) 2019 Ansible Project
 # GNU General Public License v3.0+ (see COPYING or https://www.gnu.org/licenses/gpl-3.0.txt)
 
+# CAUTION: There are two implementations of the collection loader.
+#          They must be kept functionally identical, although their implementations may differ.
+#
+# 1) The controller implementation resides in the "lib/ansible/utils/collection_loader/" directory.
+#    It must function on all Python versions supported on the controller.
+# 2) The ansible-test implementation resides in the "test/lib/ansible_test/_data/legacy_collection_loader/" directory.
+#    It must function on all Python versions supported on managed hosts which are not supported by the controller.
+
 from __future__ import (absolute_import, division, print_function)
 __metaclass__ = type
 
diff --git a/test/lib/ansible_test/_data/legacy_collection_loader/_collection_finder.py b/test/lib/ansible_test/_data/legacy_collection_loader/_collection_finder.py
index e0c3c109b9e..2ac88ca3260 100644
--- a/test/lib/ansible_test/_data/legacy_collection_loader/_collection_finder.py
+++ b/test/lib/ansible_test/_data/legacy_collection_loader/_collection_finder.py
@@ -1,6 +1,14 @@
 # (c) 2019 Ansible Project
 # GNU General Public License v3.0+ (see COPYING or https://www.gnu.org/licenses/gpl-3.0.txt)
 
+# CAUTION: There are two implementations of the collection loader.
+#          They must be kept functionally identical, although their implementations may differ.
+#
+# 1) The controller implementation resides in the "lib/ansible/utils/collection_loader/" directory.
+#    It must function on all Python versions supported on the controller.
+# 2) The ansible-test implementation resides in the "test/lib/ansible_test/_data/legacy_collection_loader/" directory.
+#    It must function on all Python versions supported on managed hosts which are not supported by the controller.
+
 from __future__ import (absolute_import, division, print_function)
 __metaclass__ = type
 
diff --git a/test/lib/ansible_test/_data/legacy_collection_loader/_collection_meta.py b/test/lib/ansible_test/_data/legacy_collection_loader/_collection_meta.py
index b14917c30e2..756cd7ac6ea 100644
--- a/test/lib/ansible_test/_data/legacy_collection_loader/_collection_meta.py
+++ b/test/lib/ansible_test/_data/legacy_collection_loader/_collection_meta.py
@@ -1,6 +1,14 @@
 # (c) 2019 Ansible Project
 # GNU General Public License v3.0+ (see COPYING or https://www.gnu.org/licenses/gpl-3.0.txt)
 
+# CAUTION: There are two implementations of the collection loader.
+#          They must be kept functionally identical, although their implementations may differ.
+#
+# 1) The controller implementation resides in the "lib/ansible/utils/collection_loader/" directory.
+#    It must function on all Python versions supported on the controller.
+# 2) The ansible-test implementation resides in the "test/lib/ansible_test/_data/legacy_collection_loader/" directory.
+#    It must function on all Python versions supported on managed hosts which are not supported by the controller.
+
 from __future__ import (absolute_import, division, print_function)
 __metaclass__ = type