Finish goods with negative and positive onhandqty in the staging shipping area

every time when I send finished goods to a customer that needs PCID to be created for each product , I am getting a new record on the staging shipping area (S1) created on partbin table but with negative value, so after 2 shipments that required PCID number for each finish good sent each on of them will have a new record in the partbin table with the bin number S1 and a negative OnHandQty. for example:

PartNumber WarehouseCode BinNum OnHandQty PCID
ssi shipping S1 480
ssi shipping S1 -200 0119932288337
ssi shipping S1 -280 0119932288345

how can avoid to create this new records and just calculate the new OnHandQty on the existing record if I am not going to use the PCID in any future?