buildscripts/validate_commit_message.py checks that the commit message contains a reference to a SERVER ticket, but it doesn't check if the ticket actually exists. There is no reasonable way to prevent people from referencing the wrong ticket, but it is possible to at least catch cases when it doesn't exist.

Here is an example of PR that was merged with the referenced ticket that doesn't exist
https://github.com/10gen/mongo/pull/38712
At the time of the merge SERVER-108543 doesn't exist, and it seems like there should have been SERVER-104853 referenced