Yes of course he said it in an itw, but when doing so much itw, during so long time, I think that even Gu or Mark can't remenber exactly which gera was used, except if itwas listed, wrote and compiled by the sound enginner, or one of his assistant.
I think that sometimes during recording sessions, Mark and Glenn Saggers try different set-up : different guitars, amps...with different recording takes
So maybe, many months later, he remeber having used a particular guitar during days, but it's not necessarily the one on the final mix ?
I always quote the itw where Mark claims that trwalerman song is played on the 54 : maybe a take of this song with the 54 exist (and maybe that's why he played it this way on tour), but of course the final mix is with the LP58.
So it's hard to say if we can believe Mark's memory every time
Same for Guy, when he answers on his forum, sometimes it is just "if memory serve", but....
Of course we will never be 100% sure, but I agree with Ingo : the schecter sound is more "metallic" than the 61 fender, so indeed Silvertown sounds far more schecter than WII