Maybe not everyone is aware - KiCad developers have switched source control from Bazaar to git (on Launchpad). Bazaar has traditional style revision numbers, therefore BZR7155 etc. Git does not have any concept of revision number, only commits which are tagged with a 160 bit hash value which are globally unique.
The git hash can be shortened to a few characters which is unique enough to identify a commit, but is essentially a random number. This is useful for developers but has little meaning to users.