It's always been the big question between 'discovered', 'first played' and 'broke' - as they are very often not the same thing.
For a minor example, a few years ago we were watching Eve's Bayoo, in the background of the party scene there was a brief snippet of brilliant unknown track - we go 'ayup what's that???' - it turned out to be an unissued (and totally unknown) Jimmy Radcliffe demo 'I'll Pretend That I'm Loving You' - only available via the obscure full soundtrack album (rather than the normal one) - we 'phoned a friend' played it off the video down the phone, got him the CD and were there when it was first played out (at King George's, Stoke) to excited reaction from DJs who were extremely puzzled to hear it dedicated to us (as we'd kept it zipped for maximum impact). It was briefly very popular, though sadly at 1.50 a bit too short (would benefit from being mixed into something longer).
Likewise John Anderson, Soussan etc etc etc turned up hundreds of landmark sounds and recognised they'd 'go' and sold them on - but the DJs are the ones who are famous for breaking them, though I guess a lot of the time a given record needed the authority of a famous DJ to attain their rightful initial acceptance.
Equally something like Ann Perry was (like many sounds) first spun at the Cats, but it needed the booming back wall of the Casino to reach its full potential of popularity.
Dx