Nostr clients are a bit confusing right now and I'm pretty sure most users do not know these details.

Clients early on could "mention" pubkeys aka others. Now they also can what I would call "reference" others following nip-21. The difference is that the former will trigger a notification to the mentioned while the "reference" should not.

Clients now replace nip-19 bech encoded pubkeys as references or mentions and it's hard to guess which of those it is.

Furthermore mentions do not require to be included in the content of the event, leading at least me to suspect that a brief addition of a mention even though I later remove it from the content might still retain the mention in the tags.

I would want my client to let me edit the "mentions" that go with my message. I want to "mention" people without referencing them and reference them without mentioning them.