And as noted, the older 75 (also known as Pre-B models) mags will work in the B models, but many mags that work in the 75Bs won't work in the 75s.
It's more of a "gun" issue than a "mag" issue, as the oldest 75s had a tighter mag channel in the grip near the top. As they moved forward in time, they started to accept the newer mags, which are very slightly larger.
The mag channel can be opened up with a flat file in these older guns pretty easily. There are instructions on a number of these forums of how (and where) to do it. Once opened up, any mag will work in an older 75.
As noted, the compact models will accept full-size mags, but not vice versa.