Never saw a TG, but have seen As,Bs,Cs and a D. These grades indicate decoration, wood quality, and the Cs/Ds have cut checkering. There was an All American model before the Letter trapguns, and the Classic Trap available now.
870s take a lot of use, but some have seen exactly that. Things to look for include:
Oversized Locking Blocks, ID'd by a CR stamped in them aft of the lug.
Peening or wear on the lug and the recess in the bbl the lug locks into.
A rough forward corner surface on the ejector.
Visible bluing wear or obvious reblues. Look at the wear on the mag tube to see if it and/or the action bars need straightening. The pattern of wear can indicate what's impinging on what.
Mine was made sometime in the 80s, I've put close to 6K rounds through it,and little wear so far. Who knows how many shots it's fired since leaving Ilion.
A contributing factor to an 870 Trap's longevity it that it fires lots of rounds, but relatively low pressure and recoil rounds. Most trap loads run 1200 FPS, 1 1/8 oz or less. These beat up neither the shooter nor the shotgun as much as waterfowl or max buck loads.
