I started this thread on Perfect union. Has links to websites and threads, and pictures on identifying aftermarket Mini-14 magazines including: USA Magazines, PMI, Federal Ordnance (PMIs with no markings on floor plate), McCoy, Thermold, Ramline, Masen, Western, Scherer. Bingham, Pro-mag, Triple K, and Eagle. Most of those are pre-ban, so it is a good resource. I checked, and opened the page without logging in, so it should work for everyone. I had 9 magazines I bought back in the day that I always thought they were PMI, but turns out through the resources here was able to determine that they were actually early USA Magazines with no markings on floor plate.
Hope this helps someone.
Identifying Aftermarket Mini-14 magazines