This is a Nazi stamping. They are still in circulation. Those date stamps are changed constantly. I work for the company that owns them. They are old as shit. We are based out of Germany and they pop up every now and then but most have been recycled.

Metal lasts forever as long as you don't use CO2.

I had a conversation with a local gas distributor one time, and he said for low pressure bottles (C02 was mentioned specifically, but idk about n2) there is no age limit on bottles, they get tested every year, and if they pass the get recertified and kept in circulation. He said the oldest one he saw was from the 1890s

In Germany bottles that old still pop up from time to time. Some oldie dying and his family clearing the age old garage or shop happens quite regularly.

Yes it is.