If your marks are the same, then your performance is seen to be the same. This is despite whether or not a grad school somehow knows the other did some topics earlier. If you continue to get top marks, there is no problem. The only way a disadvantage may arise is with a difficult class where you may struggle to grasp all the concepts firmly in such a short amount of time, whilst the other student in that case has a better ability to get higher marks.
Most courses are designed so that you have the opportunity to get high marks even if it was your first time learning it, but some set the difficulty higher and get a lower average. In those cases, the person who knew the content already may find it easier to get the stellar marks. But note this doesn’t mean it’s impossible for you, perhaps just a bit harder. It’s never this extreme, but say you had an entire Calculus course crammed into 4 weeks for some reason (which is similar to how some Uni’s cram Abstract Algebra into a single semester in my opinion), then the student who hasn’t learned it before will have to step up to a large task of understanding such a load in such a short amount of time, whilst someone who knew it already will still quite easily get very high marks.
This is a minor issue to think about; the best you can do is to think about learning as much as you can from now on. Don’t let the focus to accelerate through topics, but to understand each solidly. That’s very important. Grad schools don’t look at who knew the content in some sort of fashion as quickly as possible; they look at who knows the content most solidly at the moment! (as well as research potential). It so happens that I am probably one of the students you are talking about, but unless it really interests you, I don’t think knowing how much other people knew will help you, especially in light of what I’ve just told you. Good luck in your studies, and wish me luck in mine! =]