Well, the WD-45 was an upgrade from the original WD, hence the addition of the 45 (probably for 45 hp or thereabouts, since the WD45 was 43 belt hp).
The WD was an upgrade from the WC, hence WD instead of WC.
WC could have meant nothing, but as I remember it may have been called "all-crop" for a while. The WF was a "standard," non-adjustable wide front end version of a WC. I'd guess the "c" portion had something to do with cultivation or crop, but no bets on that. No idea what "w" stood for.
All these are my guesses. WC could have been a generic, off-the-wall designation with no associated words or could have been the next in line of a particular model designation class. Norm Swinford's book - and CH Wendell's - may shed some more light on this.