Joe, that's the action of the Auction House rather than the Proof House. They can't legally sell a gun out of proof so they adverise it as 'Stock, Action & Forend' and the barrels can be sent to a registered gunsmith of your choice in order that they can be re-sleeved or just maybe cleaned up and re-submitted. If you want the barrels they will come cut. The Proof House will return a failed gun in whatever condition it was when it failed as it still belongs to the owner although he can't legally sell it, offer it for sale or export it.
That Boss looked as if it had really had it's day. That is quite often the case with some of the older high end guns. They were bought in the days of big bags of driven birds. The main shooting seasons run for 5 1/2 months of the years; starting with grouse, then partridge and then pheasant. Some of the owners of these guns would be out shooting four or five days a week in season and may fire hundreds of rounds in a day. Those guns had a hard life. Lagopus.....