I think you can really only go on the ID's on your list, which automatically change if the buyer changes their ID. The only way I can think of to be sure is each time you add a name to the list, create a document and write their details on that and add new ones as they are added to the BBL. Of course that would be a pain if you have a high number on your list, but it's the only way I can think of doing it so you have a record. Adding the names in alphabetical order could make it a bit easier.
I've created excell documents for my stock and subsequent sales. When an item sells, I add the buyers username. If you've got something like that, you could also add the rest of their personal details. Again, that would be a pain if you have a lot of sales, but it's still a record.
