There is a big difference between Prelim and Categorical positions.
Preliminary positions are generally for 1-2 years only and are typically filled by persons needing an introductory year before pursuing other specialties (ie, Ortho, ENT, Radiology, Anesth, etc. all are required to do a Prelim year before starting their specialty training).
A Categorical position implies having a spot which will lead to the completion (providing no problems) of the training program; in general surgery this would be the full 5+ years.
Therefore, a Prelim position is only for a short period of time and there is no guarantee that one will be hired for the Categorical track. However, many persons who are unable to get a Categorical spot will accept a Prelim position in hopes of being offered a Categorical training spot the following year.
There are generally hundreds of open Prelim surgical spots each year after the match and these are often filled by IMGs and others unable to obtain the Categorical position. Not as desirable, for obvious reasons, but it may be means to an end...
Hope this helps.
