Is there a way to know if a PO was generated by a drop ship item other than looking at the line items? I saw an old article that said a “dropshipso” field was set, but it’s the only article on the internet that says that.

Comparing POs on our system, dropshipso has a transaction internal ID on drop ship POs. Regular POs don't have the field set.

There is a "createdfrom" field on the PO Line item. My guess is that if the PO line was created from a DropShip item on an SO, this field is going to contain the SOnumber or the uniquelineid identifier from the SO. the reason I think this is that when you update the PO values, those changes can reflect on the SO line as well.