Another one is Muine Bheag (Bagenalstown previously Moneybeg) v Muine Beag (Moneybeg, Donegal Gaeltacht). Per modern grammar Muine Bheag is correct, but the Moneybeg anglicisations and the living name in Donegal all suggest Muine Beag was the norm in at least two dialects.

I remember schoolteachers and even a few university lecturers long ago being quite superior in talking about caint na ndaoine in Cois Fharraige, but I believe theirs out there is the worst Irish of all. Not alone there, it seems now.