Now I have a theory that if your latest/last villager is invited by campsite, then maybe the game doesn't glitch? Of course I have no way to test this theory unless I use someone else's savefile, then do the whole amiibo thing with one of their villagers, before trying my method to see if it works. The amiibo thing requires a lot of effort though since I have to invite them, make the DIY thing they want and timeskip, repeated three times until I could invite them in. Then I have to perform my method after that villager had unpacked and settled in. It involves a whole lot of timeskip and steps which I'm too exhausted to do right now lol.
I never invited amiibos or by campsite so far, but I managed to invite Raymond correctly it's a lot of work, I'll break down the steps and it works 100%.
1. You need to have 10 villagers.
2. Say you don't know who's your last villager or you don't want to swap out your last villager. You want to swap out #5 villager.
3. Backup that save and open it in NHSE and remove the villager using the empty villager file I provided.
4. Open the game with this new save, the #5 house is empty now. Go to a Mystery Island and invite someone in, say, Rocket.
5. Fast forward one day, Rocket moves in. She is legit, she has all of her correct stuff.
6. Backup the save and open it in the editor, remove Rocket.
7. Open the game, confirm the empty house, save.
8. Backup the save and open it in the editor, add a legit villager file (don't make me try it again with a false one, might work, but I'm too tired now, if someone needs to know please step in).
9. Open the game, go to a Mystery Island, invite someone in. The plot should say the name of the villager you want in instead of the one you just invited.
10. Fast forward one day, everything should be correct. But if you want to edit in another villager you
have to use another one and go back to step 3, you have to make someone your new "last villager" otherwise you'll get a clone of the guy you just moved in.
As a side not, as I said, I also noticed only legit villagers get announced by Isabelle. That may be the "flag" that causes this? I don't know. But that's how you get a working correct villager with all the correct stuff.
