1975 was the first bathroom GFCI requirement.
The 20-amp bath circuit appeared in 1999.
However, keep in mind that most jurisdictions don't adopt a Code for a few years after it's published. So the 1975 may not have been adopted in the area you are until '76, '77, even '78. I work in a few areas that are still using the '99.
As for the remodel, it may not have been required to update it, but that would have been an AHJ call.