Seriously. I could use a Monograph on SIG Sauer P320 Magazines or a Field Guide to SIG Sauer P320 Magazines.

Why?

I own the collection of pieces to assemble everything 9x19mm and P320:

Full size X grip module (GM);

Full size Wilson Combat GM;

Full size OEM GM;

Carry GM;

Compact GM (in small, medium, and large); and

Subcompact GM (in medium and large).

Not bad for “one gun.”

I now have discovered that magazines are not as interchangeable as I thought.

The full size X grip module (GM) takes the two that came with it, plus a 21 rounder I picked up somewhere.
The Wilson and OEM work with the OEMest of OEM magazines.
The compact large takes everything. The compact medium doesn’t like the X magazines, or the after market 17 rounder that came with the full size Wilson Combat. The subcompact takes everything too, but a 21 round mag and concealed don’t go together.

Has anyone thought to make the magic decoder ring?

You have. Since you have all the pieces start diagraming it out for us. Also include which magazines have which basepads, Gen 1 and Gen 2.