Damn good question - unfortunately, Quadrastate white-label promo is one of the only ones I'm missing (both the promo and release sheet)!
Here is a scan of the white-label, however:
Well, it was recorded in November 1988, and the saxaphone was added early January 1989 (from the Filofax pages).
The date of the test pressing was 26th May 1989, with 8th July 1989 the first airing on The Other Side Of Midnight. And Quadrastate itself got released on 28th July 1989.
So, I'd guess that Gary Davies (who apparently went to Ibiza that year where he heard it), would have played it on the radio around July/August 1989?
That's just a guess, however?