Ive Had People Ask If They Can Come But Werent On The List, And I Added Them As People Declined. Nobody Thought It Was Rude At All. And Because The RSVP Deadline Was So Close They Didnt Get Invites, They Just Got Our Wedding Website To RSVP.
With COVID I don't think people would be offended.
I think people are very understanding right now so not fair to just blanket say this is rude. If you had to cap your list because of Covid, people get it. You could say something like, “because of COVID we had to limit our guests to family (and XYZ) but as soon as space opened up I thought of you and would love it you could come be part of the celebration.” Since you don’t have more invites I would call them (not text) and invite them and then email them all the details they would need.
That all being said, I’ve gotten a “b list” invite to a wedding before (in non-Covid times) and wasn’t offended at all - it was a wedding I didn’t fully expect to get invited to, so was nice to be included.