no its explicitly said that it takes two years for a tree to get Myrrh available again after you harvest a drop. just straight up "Myrrh Trees need two years to recover." that and trees from the first year are full now, even though the caravan from Marrs Pass could easily get them all, and I'm betting you come fourth year, those three dungeons will still be full despite Marrs Pass being right next to them, because this is a videogame.