Nearly every mod or armoring you can pick up from the comms vendors has no schematic, so it can't be learned.
You get to learn odd-numbered schems, such as "Guardian Armoring 11" or the like, until late in the game (appx. chapter 2+) whereas the comms vendors sell even-numbered gear (Patron Mod 12) which has no schem.
It's annoying and unfortunate, but there you go.
I got that, but I was asking mainly for the people who shout about making the Might Mod 27s and such - are they finding schematics for those, or are those drops that they're REing, or what? Purely the level 50+++ stuff that's all endgame incremental boosts - sorry if it didn't sound specific. Are they getting premade 27s, breaking them down and learning schematics somehow off that (which is the odd bit, since they're purples and you're learning purple schematics) or are they actually getting schematic drops that lets them make those?