Are already-written articles in the current turn canon?
No. You may refer to them if you like within your own entry, and you can link directly to them within the same turn, but only in a secondary reference section. From a standpoint of being a good collaborator and not messing with others’ work, though, it’s safest if players consider already-written articles in the current turn as canon and try not to break other players’ already-written work within the turn. Otherwise it would be possible to wholly invalidate other players’ work within the turn, which might be cranky-making.