The only solution is to use numbers and hp for "normal" and less important npc, and the New system for "Boss" npc.
My2Cents.
Uhm... You get that that's precisely how it works, right? Only PCs and boss type enemies are subject to the full injury system. In a big epic showdown type fight, you'll have maybe 1 enemy who uses the full injury system, 1-2 that uses part of it, and a bunch who don't use it at all.