Your understanding of the Change-Id footer sounds like it matches mine.
I’d note that it works that way presently, but the teams behind git, gerrit, jj-vcs, and a couple of other relevant stakeholders have an email thread going in which, from what I understand, they discuss standardizing on the approach taken by jj-vcs:
https://lore.kernel.org/git/CAESOdVAspxUJKGAA58i0tvks4ZOfoGf...
This is based on what I remember (haven’t used gerrit in a while), so it may not be accurate.
I used gerrit in my previous job and miss using it. Would definitely prefer it over GitHub which is more popular (and convenient of course, can’t deny that).