(1) Advanced vs Categorical. Some positions have both. Advanced means you matched into your residency of choosing (Rad-Onc, Optho) but THAT program has no intern year for you. So you have to go find somewhere else to do a year. Categorical means they not only have the residency of your choosing (Rad-Onc, Optho), but they also have an intern year for you.
The advanced person will match preliminary surgery, University of Surgery AND match Dermatology, University of Dermatology
The categorical person will match Radiology-Oncology University of High Step 1 Scores
(2) Fail to match. Some one who has ONLY a prelim program is some one who failed to match and likely scrambled. Since basically ALL spots except family medicine (likely not their intended career choice) and prelim surgery were taken, it is better to do a year of internship, then try again, than it is to do nothing and try again.
Some programs take prelims so that interns intentionally exceed categorical spots. This allows programs to fire categoricals and take prelims. Great for the prelim, terrible for the categorical that got fired.
Some programs will take a prelim PGY-1 graduate and hire them into a PGY-2 spot at a different hospital. This is rare.
Basically every other prelim-only match is going to do ANOTHER year of internship as they match this year "as they would have" into a categorical program. That first prelim year was just to say "i practiced medicine and I done good, let me in!"
This person will read Preliminary Surgery - University of Didnt Match, sorry dude