I agree with shiftingmirage that errors that may have derailed an applicant the first time around can be corrected (such as applying early, better targeting applications, more clinical experience) but I suspect (I've not seen the data) that reapplicants as a group are less likely than first time applicants to be admitted somewhere. There are often "fatal flaws" that preclude admission the first time and often those are not remediated enough to justify admission the second time around. This can include really poor grades and scores, odd behavior or affect during the interview, toxic letters of recommendation, and poor motivation for medicine.
I think that AMCAS keeps track of where you've submitted an AMCAS and when. A space on the first page of the AMCAS application that I see has a field labeled Reapplicant: and it will populate with year(s). I think that AMCAS does that automatically but I don't know for sure.