Sales orders and Customer Purchase Orders are related - you can't initiate a sales order without a customer purchase order. Sales Orders must have a unique Sales Order ID, and Customer POs don't, since different customers may have ID collisions - Otherwise, they're identical.
I'll put in some other creators.
Collection issues are mainly due to poor book/unfamiliarity with language/lack of instructor assistance.
I did do some code updates last night, but forgot to replace the old version with the new - so I'll be doing that tonight, along with a (very primitive) GUI. Right now, the tendrils from the GUI are starting to reach out towards the tendrils of the data stores, but neither are seeing each other yet.