The letter series omitted in 1977-82 are partially known.

80 prefixes were omitted, including light truck series,

but only these 45 are verified:

 

AAS, ABM, ADA, APE, APU, ARS, ASS

BAD, BAN, BAR, BAT, BRA, BRP, BUG, BUM, BUT, BVM

CAD, CAN, CAT, CUR

DAM, DDT, DEM, DTS, DUC, DUD, DUF, DUK, DUM, DUX

PED, PET, PEW, PSS, PUE, PUG, PUP, PUS, PUU, PUW, PYU, PZF

RAG, RAT