Add further guidance when documenting versions

doc/development/documentation/styleguide.md

@@ -1244,6 +1244,20 @@ a helpful link back to how the feature was developed.
 NOTE: **Note:**
 Version text must be on its own line and surounded by blank lines to render correctly.
 
+### Versions in the past or future
+
+When describing functionality available in past or future versions, use:
+
+- **Earlier**, and not **older** or **before**.
+- **Later**, and not **newer** or **after**.
+
+For example:
+
+- Available in GitLab 12.3 and earlier.
+- Available in GitLab 12.4 and later.
+- If using GitLab 11.4 or earlier, ...
+- If using GitLab 10.6 or later, ...
+
 ### Importance of referencing GitLab versions and tiers
 
 Mentioning GitLab versions and tiers is important to all users and contributors