i encountered an interesting position recently. we play A=att, K=CT/UB for Q, Q=CT/UB for J, also J denies i held a strong hand with heart one-suiter and led HQ against 1NT opened and doubled, which was won by decl with ace. when my p was in hand he was unsure whether he should return heart (good if i had KQ10xxx), or side suit (good if i held AQJxxx) to avoid me getting endplayed. now, inferences could be drawn from declarer play and discards but anyway we came to the conclusion that it would be convenient that exception is made to "jack denies" when it is known that attacker is long&strong in the suit led, so that J shows AQJ