diff --git a/.github/CONTRIBUTING.md b/.github/CONTRIBUTING.md
index 26748164..6e7211b2 100644
--- a/.github/CONTRIBUTING.md
+++ b/.github/CONTRIBUTING.md
@@ -23,3 +23,5 @@ Repositories not hosted on GitHub are fine, but they won't have a
 
 The last commit times are automatically updated every hour.  You don't
 need to make new PRs to update your entry.
+
+Note: if you're adding a repository to previous years, such as 2019 or 2020, you'll need to provide the full link format, as in the non-GH example above. This applies to both GitHub and non-GH repositories.