Warning, big spoilers ahead! Please read this only if you already finished the books or don't plan to read them (which would be a shame ;)
Several times during his journey Roland knows things for sure but not knowing why he does. "I just know it". We clearly understand at the end that
as it's not the first (and not the last, the wheel of Ka turns...) iteration for Roland, he knows these things from his previous living of the story.
However, his companions doesn't seem to have this kind of inter-trip memory (unless I don't remember). Should we then deduct that it's the first occurrence of the trip for them (with the change from the previous trip being the three cards/doors?) or only Roland remembers partially as he's the only one entering the tower's last room?
Title of this question should have been something like
Is it the first trip for Roland's companions?
but it would have given too much for the ones reading the books.