I've checked my BR timtables entirely from 1988-1991 and can find no Glossop trains that continue beyond Piccadilly.
I have spent some time on research since this thread was first posted, so this is why I am later than expected in giving a more fuller reply.
There would be no reason for these units ever to have progressed to Deansgate. I cannot trace any workings from the Hadfield/Glossop area to there after the change of power supply was implemented and there would have been much crossing of the lines from the junction at Ardwick to the through lines at Manchester Piccadilly.
It would have allowed DMU's from Hadfield/Glossop, should this have been allowed, to access the lines through Patricroft and through Altrincham, but there was no known demand for through running on either of these routes, especially since the closure of the Woodhead route, which could have carried freight to both of these two lines from South Yorkshire.
The only DMU units in those far-off days of the 1980's, which only stopped at Altrincham and Sale and then passed through Deansgate, was the Chester - Northwich - Manchester service, which used to hurtle past me at Navigation Road station , much to my annoyance, during the morning rush-hour.
