I'm not sure about Stranraer sleeper routeing - I thought it went via Mossblown not Glasgow - but I remember using the Carlisle attachment on the Glasgow to Euston sleeper around 1990.
You could get the last local train of the day from Dumfries and then check in to the sleeper in a bay platform at Carlisle around 11pm. Sleep was cruelly disturbed an hour or so later when you were violently propelled across the station and rammed into the rear of the Glasgow to Euston train. Today's Caledonian Sleeper shunts are timid by comparison.
I can't remember if it worked in the same way in reverse. I also recall using the Edinburgh to Plymouth sleeper calling at Carlisle late in the evening, so there were plenty of night trains serving the area at the time.
The history of the Paddy as it was known, is this.
The Stranraer Boat Train to London started from London Euston in the 1920s I believe. It was the 10pm from Stranraer and went via Galloway to Dumfries, then WCML to London.
After June 1965 when the Port Road was closed it went Stranraer - Ayr - Mauchline - Dumfries then to London.
When the curve was closed in 1976 between Hawkhill and Blackhouse Jn in Ayr (thus preventing use of the Falkland Jn - Mauchline section) it was re-routed via Kilmarnock and at the end via Glasgow. (Source CJ Fryer Girvan & Portpatrick Jn Railway)