When I bought my boat (in 2013) it had the original sales invoice from the builders and the invoice relating to its second sale (I was the third owner).
These documents, unlike the service history, BSS etc, were not made available to me until the purchase was complete. I thought that was fair enough, I had the brokers word that they existed and that they constituted sufficient proof of the seller's ownership of the boat, I didn't think that the actual figures were any of my business until I owned the boat (perhaps not even then).