Attributions of the first two sound like pure poppycock. I have no doubt they were both in the US Cartridge Co. collection since they apparently appear in the old catalog, but I'm fairly certain that is the full extent of their historical connection.
http://www.bonhams.com/auctions/20973/61168/#q1_1=cannon&m1=1&b1=listf If anyone is thinking of bidding on no. 3264, the Hotchkiss 2-pounder B/L,
make absolutely sure you know what the actual date of manufacture of the gun is, since most of the American Ordnance guns are post-1898 and thus are Destructive Devices per BATFE, and must be registered in order to be owned or transferred. The auction catalog is silent regarding the date of this piece. Last time I checked, there was no exemption in place for post-1898 Hotchkiss 2-pounders, even though the same model made in 1898 or prior is officially a non-firearm.
The auction estimate is way high for a 2-pounder with pitting both inside and outside the barrel, IMHO.