It is difficult to provide an exact no for the number of seats that will be available fot admissions under 50% .

a total no of 128917 candidates appeared for NEET pg 2018 so acheiving an all india 50% quota category SC rank of 439 is a pretty good achievemen. 

If we take a look at seat allotment results from past two years SC candidates who have obtained category ranks in 400-500 range have been able to pursue all the major specialisations across MD,MS and diploma coursesin govt medical colleges across the country.