A dealer can shred the 4473 document after twenty years.
He must maintain his bound book records for the life of the business and surrender all of them to the BATFE when he closes shop.
No matter, the BATFE has at least thirty years of unproccessed records on hand.
I know this because I went out of business in 1994 and have since then received trace calls on a couple of firearms that I have to refer them back to their records division since I no longer have the bound book records of these sales anymore, they do.
They traced the guns from manufacturer to distributer to dealer,(Me), but could go no further.
I only kept my sales receipt books for ten years after I went out which is the limit of the law in Illinois so I couldn't even refer to those as a starting point for their traces.