Old CO2 Cylinder question (Legality)

I bought some old CO2 tanks and ball lock kegs from a bar that closed. I went to the local Airgas to exchange the 20lb CO2 cylinder and they asked about the tags on the tank from another gas supplier. They took it in trade once I explained the situation but when I asked about the larger cylinders that I also got (2-50lb) the guy said that those needed to be returned to the company since these were probably all from an old lease. The bar closed in the early 90's so these have been sitting around for a LONG time.

I am searching all over the net but I think that the company went out of business. Does anyone know what I need to do from here? I would like to either keep and use it, or trade it off but I obviously dont want to do anything to screw anyone over in a trade or anything that is potentially illegal (Airgas rep statement).

Thoughts?

Thanks!

I bought an Oxy/Acetylene torch set at a farm auction. I got the same story when I tried to get them filled at the welding supply that has filled/exchanged my tanks for years. The company who's name was stamped on the tanks went out of business when I was still peeing the bed.
I may have dropped them off at an actual welding shop and they might have ground off the collar and company stamps and "reconditioned" the tanks. If that happened, I would then be able to take them anywhere to get them filled (not exchanged).

Just sayin'