Whilst 1M16's timings on the WCML are a lot tighter than 1M11 on Sunday night there's always a 30 min "Engineering Allowance" for all the Sleeper services to allow for possible Single Line Working (SLW) between Carlisle and Carstairs if this is required for any works - it's why the services depart 30 mins earlier on a Sunday. However, the SLW rarely happens and so there's 30 mins that can usually be made up pretty easily.
You can see it in the RTT info against Cove Signal Mc862 (just north of Gretna) - in the far right column - 30 (mins) engineering allowance plus 3 (mins) pathing allowance.
http://www.realtimetrains.co.uk/train/G60102/2018/03/04/advanced
As a result of this 33 min "gimme", 1M16 was already back on time (or thereabouts) by Gretna.
There were the overhead line issues around Crewe whichimpacted 1S26 and 1M11, but they were resolved by the time 1M16 arrived in the area.