In my opinion, since betas by definiton are fluid, there is little ROI in grooming their docs. If betas trip you up too much, best to avoid, I think.
About the still in use examples, I'd not expect release docs, if that's what you're referencing, to demonstrate parity w/betas, instead waiting for next release. Otherwise, monitor the beta release notes and sniff comments in code as applies.
Normally, the suggestion is to file bugs against the docs, but with betas, those geese are already out of range and new ones are just coming into view, Apple is working on next gen vs. what devs see, so...you might be asking for changes to beta version docs that are EOL.
Anyone using betas should be firmly grounded, able to self-support, with appropriate expectations. If you need painted lines on the road to stay in your lane, you might want to take a different route 😉