I didn't know you had written those pages, JF, amazing job by the way. The only way we know for sure what guitar was used on My Parties is ask either Guy or Mark himself.
Regarding On Every Street, I'm with PensaGhost as it seems pretty certain he used the Schecter and this is more evident by the fact that he used that guitar to play it live.
asking Guy or even Mark does not always give you a 100% right answer
I remember for the KTGC album, Guy provided some infos on his site, and Chuck provided infos on Mk news, and there were subtle differences. Who was right ?
another example, Chuck forgot to mention Mark's guitar on sucker row, that's why I firstly tought it was Richard who played the solo, but it was a Chick ommition
and last but not least, I have an interview where Mark says that Trawlerman song is the 54 strat, and we all know it's the 58 LP. (strange though , he played that song live on the 54 in 2004, so maybe he tried different guitars, on different takes in studio ?)
so, even people who contribute themselves to the recordings can be wrong, and don't blame them, it's impossible to remember exactly what gear they used on all of these recordings
so appart from ou ears and some speculation, it's sometimes hard to be 100% sure
as for the song OES, maybe I was misunderstood, but of course I also think that it's the schecter on most of the song (lead licsk and outro riff), but the lick at the end of each verse (with tremolo, and played with a pick) is a different guitar track (I have listened all albums on headphones to write these pages), so maybe it's the same guitar (the schecter) but maybe not, that's all
And imho, we will never know for sure, even asking Mark or Guy