Save the date then no invite

I don’t know what the difference is between a day guest and an evening guest, but I would handle it the same way no matter what. If you don’t want to go, decline. There’s no need to tell her that she’s been rude, she likely knows and doesn’t care.

If you didn’t get an invite there’s nothing to rsvp to. I’m confused.

If I understand this correctly, which I might not, do you mean you received an online invitation that same evening??
If that's the case, maybe they had an oversight when sending out invites, or maybe your invite got lost in the mail. Either way, I wouldn't let it bother me. If they sent you any form of invite, you are invited, and if they didn't want you there, they wouldn't have sent it. Granted, it might have been that you weren't on the final guest count, but even if that was true they obviously do still want you there now.
I know not everyone will agree with me, but I think its only fair to give them the benefit of the doubt seeing as how chaotic wedding planning can be

I'd say decline if you don't want to go, and it's up to you what kind of karma goes along with that. If you're declining b/c you think they are rude and you don't want to be around them, is there really something extra in letting them know? I'm all for a petty party sometimes, but it can be a lot of negative energy that doesn't help you, doesn't help her, etc. Just no point.

What I definitely think is nuts (which seems to happen ALL THE TIME based on what I've read on this crazy website) is people go to weddings even when they have the distinct impression they aren't wanted there *and* they don't want to go. That's like a lose-lose, people. She's paying for your seats/ meals, you've gotta get a gift (or at least travel or w/e) and then both have all these unpleasant feelings about each other. That's just too crazy - and I think it's something wedding specific.

If she invited you to brunch this weekend near your home (but just far enough away to be a major inconvenience), would you go? Like somewhere you'd have to park, take a train, wait, transfer lines, and then get an Uber. If your answer is eff that noise - don't go to the wedding.

I’m so confused. What do you mean an evening invite and a day guest??

If you don't feel you were treated nicely by the couple, it's okay to simply decline. I wouldn't say anything extra!

Also confused. Are they having a day wedding. That everyone does not go to? Then an evening reception, for everyone? If that is the case, they may not have sent all of the invitations may not have gone out at the same time, or had the same reply date. Don't not go because you feel slighted someone else got invited differently. Frankly, it is not a guest's business to ask around about who was invited to which wedding events, engagement, shower, ceremony, reception . Or when. Though I understand you just thought maybe your invitation went astray . But if you mention it, it looks rude, like you are checking on them. And what is to be gained by it, besides bad feelings? Nothing. They have invited you to the evening portion. It is rude if that is after dinner, if there was a dinner. Tiered reception. But not rude if earlier was only a ceremony, or a ceremony with cake and punch for church people not going to reception. . . In the end, go if you want to be with here. Don't go if you do not want to be there. Or if you feel insulted. But there is no point in telling them anything besides, I accept, or I decline. If you are really ticked at the way they did things, buy them an etiquette book not just on weddings, but all areas of social manners. And write on the card that you hope they can use it for all their social entertaining. And do not mention they should have gotten it before their wedding.

I would contact the couple. We had several invitations that only just came back undeliverable, a week after RSVPs were due. If they sent a save the date, I would contact them.

I had a least a couple of invites that weren't delivered for a relatively small group so I resent them. I wouldnt overthink it but go if you want to be there and decline if you dont.