Hi,
So sorry, I mixed up some emails again and a few tickets were left behind (including yours).
I don’t see an obvious issue with the first code. However that only applies whenever the indexing is done via cron/cli or via the back-end with the “Continue/New index” buttons, as applies to the piece of code that gathers the posts to index.
Your second solution looks clean too, it should work – I would still keep the first code active as well, so the 3 snippets to gether should cover all the cases.
Very soon there will be a new upgrade 4.28.3, which will have a brand new cache interface with a new caching method: “super file cache” (very fast, almost instant direct file access cache).
After that I think we are moving towards 4.29.0, where I want to rework the index table interface (including the indexing methods) and also add an option for custom field exclusions – or at least a unified hook for rules if the options turn out to be too complex. That will hopefully replace these snippets, as right now it is just way too much pain in my opinion. I really want to improve the whole indexing thing in general, right now it is way to cluttered for new features.