you seem to be correct. 12 sleepers and 3 3a coaches as indicated by lower berth quota...
Accommodation Availability Enquiry
12792 PNBE SC EXP 10-2-2013 PATNA JN SECUNDERABAD JN * Lower Berth Quota
S.No. Date (DD-MM-YYYY) Class - SL Class -3A
1...
more... 10- 2-2013 AVAILABLE 24 AVAILABLE 4
2 11- 2-2013 AVAILABLE 22 AVAILABLE 4
3 12- 2-2013 AVAILABLE 23 AVAILABLE 1
4 13- 2-2013 AVAILABLE 24 AVAILABLE 6