Right, more problems with Audit, in addition to problems mentioned previously. Although Updates to Documents have version numbers, updates to ListItems do not:

Interestingly, Deletes still have a version number. But there really is no version number recorded for updates…

… even when there is Versioning on the list:

Further, although previous versions of Documents have a url which includes the _vti_history folder, previous versions of ListItems do not – instead they just have a VersionNo GET parameter:

In the VersionNo paramater, the Major version is (VersionNo DIV 512) and the Minor version is (VersionNo MOD 512) – thanks to Dink for the hint on that part!