Recognition feels different when it arrives after the helper has stopped expecting it.

Thanks arriving late meets a different person from the one who did the work. By then the helper has usually finished waiting, filed the episode away and adjusted their sense of what that relationship is, so the acknowledgement lands in a quieter place: touching, sometimes, and sometimes oddly beside the point. Neither reaction is ungracious. It is just what happens when a feeling has already been put down.

If you owe someone thanks from years ago, say it anyway and say it specifically. And expect a gentle response rather than a bright one; you are giving them something they had stopped needing.