usually off-schedule trains don't get priority, this is what i have seen and experienced also. examples, late running NDLS-BBS Rajdhani overtook by NDLS - ALD Duranto, late running DBRT Rajdhani looped for the gang of six high speed trains. Brahmaputra Mai overtaking late running Shiv Ganga, Swatantrata, Magadh, Rewa & Purushottam and etc etc.