Huh, I grew up in the South and never realized it wasn’t normal to say tuna fish sandwich. I guess it doesn’t really make sense, but I still kinda like the ring of it

It depends how you’re counting I think. If you’re just counting things, you would normally just say the number, “the 100th widget” or “the 100th day”. No need for any other descriptor. But if you’re counting things relative to time, I would say “100 widgets later” or “100 days later.” Next is very specific since it refers to only the thing directly after the current one, so it isn’t really used for high amounts of things.

I don’t have a reference since this was never directly taught in any of the schools I went to. This is just how I’ve always heard other people say it.