Sir, Last rank at Jodhpur, Patna and Bhopal AIIMS crossed 16000 in SC category last year (2017). Were these in open counselling.

Yes they were either in 3rd or open counseling. To note that it's the SC Rank that matters more because the corresponding all India rank may change.
There are 121 seats as of now. A rank twice the number is a safe zone and admission is guaranteed. But above that risks increases and so lesser the chances.
I remember a friend of mine with 125 SC Rank didn't get in AIIMS 2016. The seats were 100 almost.

Thanks