As I noticed iSoftware Updates / Twitter iSoftwareUpdates enthusiast, the seventh beta build of macOS Sonoma was released at the end of August, the code of which ends with "a". Traditionally, the final builds move in the reverse order of the alphabet: that is, "c", "b" and "a" come out sequentially. The closer the letter is to the beginning of the alphabet, the closer the assembly is to the release one.
For comparison, the seventh beta of macOS Ventura last year came out a week later and ended with an "f". But in the case of Mojave in 2018, the seventh beta was also released with the end of "a", and this was the last year when the iOS and macOS versions were updated simultaneously in September. Here's what the macOS release schedule looks like over the last 7 years:
Bloomberg analyst Mark Gurman also notes Apple Is Set to Embrace an iPhone Charger Change It Didn’t Want / Bloomberg that the release of iOS and iPadOS 17 this year will also be simultaneous — unlike last year. The release dates of the new tvOS and visionOS have not yet been announced.