The following is an example of anesthesia programs and their corresponding prelim or transitionals (also throwing in an example of programs with both advanced and categorical spots)
Rank 1 - Program A categorical
Rank 2 - Program A advanced
-- program a transitional
-- program b transitional
-- program c prelim
Rank 3 - Program B categorical
Rank 4 - Program C advanced
-- program c prelim
-- program a transitional
..............
Rank 20 - Program a transitional
Rank 21 - Program b transitional
For each advanced program you get a corresponding supplement list. This list can be changed for each advanced program if you choose to do so (see rank 2 vs rank 4). The last example is something that people should keep in mind. If they don't match at any anesthesia program, they can at least secure their 1st year spot by adding the prelim and transitional programs at the end. If you dont add prelim or transitional programs at the end of your primary list, the match algorithm will assume you would rather go unmatched.