I think your understanding of how licenses work on iNat is correct. However, we can’t control how third parties update their own records when your license choices on iNat changes, and, at least to me, it’s legally unclear whether changes to your choice of license are intended to apply retroactively. If using CC-licenced content comes at the risk of being sued for copyright violation in the future when the content author changes their decision on licensing, I’m sure that would make the risk of using CC-licensed content too high for many.
In the specific cases you cited, GBIF stays in sync with iNat on a weekly basis, so if you change your license choice for all your observations, GBIF should pick up on that in a week and remove any records from iNat it had under your previous license choice. I’m not sure how iRecord gets data from iNat. We don’t generate a pre-made archive for them like we do for GBIF, so presumably they’re using (or once used our API). Maybe they only sync of up yearly, or maybe they don’t sync up at all and they retrieved the data in a one-time event.
Regarding duplication on iRecord, that’s between you and iRecord, so you’ll have to reach out to them.