I think you’re wrong here. They would not be in the NRMP data if they transitioned, they would only be there if they re-entered the match and matched a categorical pgy-1 spot. Pgy-2 spots are found outside the match.
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The term "outside the match" is actually a misnomer. Programs may fill open spots "outside the match" but everything still gets processed through the NRMP*. (The program would show up as unfilled on the NRMP but they would not be conducting interviews, etc.).
If you are in a prelim surgery program, you re-enter the match with the goal to get into ("
transition" into) a categorical spot (most often as a 1st-year resident, even though you would be a PGY-2). If you don't get into a categorical slot, you do another prelim year (if your institution allows it) or switch into another specialty altogether.
If there are open PGY-2 slots in categorical programs, you, again, go through the NRMP to try to get into that slot (although this rarely actually happens because programs usually fill those very rare open PGY-2 slots internally but it still has to go through NRMP).
The 64 number includes OMS-IV seniors who got into a categorical program
and prelim students who re-entered the match and got into a categorical program. Thus, if you do some rough math from unofficial published match lists (which are never fully accurate, btw), one would see that about 35-40 osteopathic seniors matched into a categorical ACGME surgery program and about 15-20 DOs in preliminary surgery programs were able to get into a categorical program.
* Fun fact, historically, the
scramble was the only match "event" that was done outside the NRMP but that was discontinued in 2010 and replaced with the
SOAP, which is now also regulated by the NRMP.