Scared Silly
Contributor
You could try getting the alloy information, maybe on the Luxfer site, that shows that your tanks are in fact made out of the newer alloy. Print that out and bring it to the shop. Unfortunately, some shops just have an ignorant approach to filling tanks, but it's their compressor and you can't argue with it.
Better off taking the DOT advisory:
Notice No. 94-7; Safety Advisory; High Pressure Aluminum Seamless and Aluminum Composite Hoop-Wrapped Cylinders
as it has a bit more authority.
Also when I have gone into shops that have decided not to fill cylinders with what I consider arbitrary and capricious rules* I call the mfg of the cylinders they have in the store and have a chat regarding their ignorance.
*the only rule I am willing to accept is not filling cylinders made from 6351. But the rule of not fills for cylinders over 20 years of any type is BS.