12142 could be that single difference..12141/2 is always on top priority in ECR,thanks to comparatively less TAT @ Patna End and being a long distance prestigious train..
The only reason for such runs of late running Shramjeevi in its home can be assigned to its large no. of halts as compared to On time Kurla,Secunderbad & Kota Exp in PNBE-MGS section..