I was in the identical situation to you a few months ago. I was picking up some tools I bought second hand from a recent widow and while loading them up she asked if I wanted her husband's old 'welding stuff'. It turned out to be an oxy-acet setup from the '60s. Really nice torch and regulators etc. The tanks were marked as Air Liquide, a gas supply chain here. The tanks were way too big to be owned outright, plus they were marked with the AR name, so I offered to return them to the gas house for her, to avoid her paying an annual fee (I assumed her husband had been paying an annual lease).
When I brought them in the guy said there was no record of these tanks in their system as they hadn't been brought in for a refill in at least 30 years. It was likely they never had! Guy probably bought the torch, tried it a few times, and it sat outside in the shed ever since.
I asked about safety concerns, recertification, what to do with 'em, etc. He said if I returned them, they'd empty the tanks, refill and return to circulation. BUT if I wanted to keep them and use up the gas....by all means. So I left with two good tanks, plus an offer for 20% off my next MIG refill if i bring these tanks back to him.
Like the earlier guys said - these have value! If you use gas of any kind, you can probably get something out of them at the gas supply house.