Why? There were seven public betas and two release candidates alone – not including any internal alphas and betas.
No, there was only one RC and it wasn't even called an RC in Software Update - only the release notes gave that away. Beta testers had to guess. The so-called second RC is the exact same build number (23A344) as today's release. You read that right - in the last week or so, Apple haven't changed a single byte in the code; they just went ahead and shipped out RC2 as Final anyway, despite all the reported bugs acknowledged by Feedback Assistant responses or marked-as-dupe.
They even forgot to turn off Safari paint debugging, for heaven's sake. That's why you'll sometimes see bright red flashes when Safari is drawing things - most noticeable on slower machines or with large amounts of swap bogging you down.
So, new bugs were added from RC1 to RC2 because Apple, then RC2 gets released as the final version anyway, and they even forget to remove some of the debugging code, all to apparently hit a release date that's about one month earlier than the usual already-rushed annual release cycle.
It's total amateur night over there.