Hi Anne-Claire. It looks like you made all the searches I would have made, though I did look through the crown marks again just on the chance that two sets of eyes are better than one. Not this time though, I didn't see this impressed crown either. Since there doesn't seem to be documentation for anyone but Heathcote making this pattern it would seem at least likely that this mark is an unrecorded one for Heathcote, but we can't be sure. Another instance of just waiting and hoping for more information to turn up!