Black Pearl respawn rate is very low

Black Pearl has been made more rare since R29, and I seem to find it only in swamps now, where the nodes I know about are already harvested 90% of the time when I go to them. This is true even when there are no players about and when all other resources (including trees, cotton and mandrake) are available to be harvested. Sometimes I have suspected certain nodes to be in a static harvested state because I have never seen them unharvested . Of course, it is easier to spot new harvested nodes than unharvested ones, but my experience with the nodes I already know the location of leads me to believe that they have a different cycle than other spawns. If this is intentional to make black pearl a desired commodity, I will continue to purchase my supplies in the hopes that the price won't increase exponentially if NPC merchants stop selling it.