But posting here, we are effectively 'licensed' under the terms of the site, correct?
Yes.
Essentially, the site operates under the FUP... except that the site is actually owned by FFE. So, really, by posting here, you're licensing FFE to continue to host your material.
So effectively, if I wanted an all-Traveller license for everything including T5 and MgT 2E, I would have to have both an FFE AND a TAS license?
Yes, but...
Would the terms of those licenses preclude my including back stats for previous versions?
Yes. The TAS license precludes releasing the same material elsewhere.
So, essentially, your choices are:
1) FUP - no money, but CT, MT, TNE, T4, T5, HT, GT, and GTIW allowed. Post here, or on your own website, or on a file sharing service.
2) OGL - money, but only MGT 1E or T20, and can't actually note the compatibility
2a) OGL - make your own corebook based upon MGT1E and/or T20... money, but still can't note compatibility.
3) T5 License. Negotiate terms with Marc and his Lawyer.
4) TAS license. Money, but technically only MGT2, and can't rerelease the material anywhere else.
5) Post to COTI - No money, can rerelease elsewhere.
6) Genericize it. No stats for specific named systems.
I can't think of other modes, but IANAL.
I do know that Marc wants all official licensed T5 material to revert to him eventually.