Am I right to say that in fact SPWaW was in fact based off of the SP3 code, unlike WinSPMBT and WinSPWW2 which were based off of the SP2 code? I believe this is the case, despite that SPWaW didn't use SP3's scale, and it might mean that they hold the copyright to the code now.
yup, you got it right, AFAIK. Matrix Games have the rights to the SP3 code. Sometime ago they were going to make a SPMBT equivalent, but that went nowhere