guessing how NDVO works is a million dollar question...but here is my penny...
NDVO at times has expedited few applicants who are at the end of the process so that the applicants medical dont expire. at times even extended medicals for one or two weeks. this is completely at the discretion of the Visa Officier. Lets say most of them are accomodative - but you never know.
However, for the question, are the applicants given any spl preference since they did their medical 2-3 months ahead of time - Not really sure.
There is a huge batch of Dec medicals - jan applicants waiting to go to In Process while few Jan medicals - Jan applicants have gone through for In process. Let us just hope all the guys in between still on AR - directly jump to DM. ..so much for guessing the pattern....
Good luck everyone