i thought it might be a sound which contains a rhythmic back-beat which came to being in the late 60s with a complimentry bass riff which itself evolved into 'disco' during the 70s... but...
with this rhythmic back-beat and complimentary bass riff there has to be an ingredient of 'soul', i.e. vocal melody or harmonies etc. etc.
if that makes sense, a modern oldie may mean any sound containing the afore that has been played out on the scene whether from 70s, 80s, 90, or this century which may leave the field open from the carstairs to kenny thomas.
or am i whizzing against the wind here?