Ah, I think I see ... so it really is platform 14/15 ... but they've labelled it 13/14 because otherwise, anyone looking for the handicapped elevator to track 13 would never find it, and then loads through the platform 14 back door of the GO Train that everyone else uses Platform 13 for ...
... yes, that's what I kept telling myself ... that it didn't say anywhere I wasn't allowed to go there. It's a great place to wave goodbye to people on VIA trains! Though platform 12/13 would have been almost as good.