Green’s Dictionary of Slang

a nonsense date representing a very long time (ago).

1970		T. Clayton Men in Prison 250: Nineteen canteen. Long time ago.
1979		F. Norman Too Many Crooks Spoil the Caper 165: Some faces are gonna wind doin’ nineteen canteen, banged up, in the laggin’ station.
1991		L. Lochhead Bagpipe Music 40: All brains, nae bloody common sense . . . So. Five weans. Man that’s no worked since nineteen-canteen.
1996		I. Welsh Ecstasy 209: An unattractive divorcee of the parish of Leith, integrated into the City of Edinburgh in nineteen canteen.
2004		L. McLean Shimmer 25: [...] fried squid that Jimmy Chang’s made for me every Friday night since nineteen canteen.