These seem to be pretty staightfoward.
NEWER or POST-DEREG CARRIERS:
WN=Southwest--this is easily confused with Western
OQ=Air Florida(I think)
TZ=American Trans Air
There's a bunch of others, I can't even think of.
And here are 2 that are really confusing:
KW was not for Kiwi(USA), but Carnival. KP=Kiwi
Why is this?Jetblue- was JB taken already? or JE or JL
B6 makes no sense!
Spirit could be SP or ST. I think SR was Swissair, right?
Who makes these codes? IATA, my guess.