From this patch https://parsley.mongodb.com/evergreen/mongodb_mongo_master_commit_queue_test_api_version_compatibility_patch_0df546e44f95bb8281e452a3f672a13c7e5c7315_64778b179ccd4e7f6379be6a_23_05_31_20_25_13/0/task?bookmarks=0,2671,2692,2936&shareLine=2670

I believe that starting after the 7.0 branch cut, we haven't been checking IDL compatibility against old releases because after SERVER-70963, we only check the latest released versions of latest, last-continuous, and last-lts. At this point latest = 7.1, last-continuous and last-lts = 7.0. However 7.0 is still marked as pre-release, and any earlier git tags for 6.3, etc aren't checked because they're less than 7.0.

Theoretically, once 7.0 is released then this would be fixed and the current development branch for 7.1 would be checked against 7.0 and any stable API errors would be caught, but in the meantime there could be incompatibility errors that are put into master that aren't caught and would need to be fixed later (for example, in the patch linked above there was an incompatibility that was not caught by the script, that was caught when backporting to 7.0 here)