Just tell them a weird Dutch fellow did it. 
Eh.... I've been using the 'Dutch' excuse for why the PzH 2000 is such a temperamental piece of crap. Not sure I want to extend it to gaming, the place might get carpet bombed by NATO...
Wait a second: Gothic gets updates in Imperial Armour books? Every one, or just X? Are these officially acceptable (tourneys)?
3 and 10 both had BFG material, IIRC. Every now and then IA will have a section of BFG scenarios, though so far X is the only one with ships and fleet lists not found in FAQ2010.
As far as permitted... it varies. The real stumbling block is the IA X fleet lists, which have two points that seem to get under people's skin. The first is that there's no ship requirements (x cruisers for a BC/GC/Battleship, etc.) The other is that it allows ANY IN Cruiser/BC to be taken, bypassing the Jovian's Special Rule, meaning it can be taken with any combination of cruisers from other lists, as well as making the 'Reserves' rules for IN pretty much redundant.
My understanding is that most tournaments will allow the Character ships to be taken as a reserve, since they all have special rules prohibiting more than one.
