GT 4 digit serial - anyone know the era of these?

[mark 2]

Yo!  Got a GT Pro f&f, serial on drop out......number 4 on its own to indicate Pro then a 4 digit serial. On other GT's I've had from 82 - 84 they've had the other formula serial, month, year and production number  eg, 7821234, 7= July, 82 = 1982 and 1234 for how many made. Anyway.........trying to found out more of the era f the 4 digits. Common sense says 81 model, but can anyone confirm? It's got a straight cut off top tube, no holes in either drop out, non drilled forks. Anyone know arses from elbows? Thank you 

The info on bmxmuseum doesn't go back this far btw.

[dj_benice]

pretty sure that's right, my 81 is a 4 digit stamp, something like 5817.

[mark 2]

I think I'll stick with the 81 theory then, thanks Pete