"after the next hydro" do you mean when the hydro is out of date? Also, assuming you are talking about AL tanks.
I worked in a very busy shop in SoFlo not too long ago. It was very frustrating to get everyone on the same page, aka knowledge, as sometimes the fill bro was either swamped and needed help or not there. So we instituted a policy on AL tanks...No-go on any older than '90. No more studying tanks and their history, and no more filling tanks that we should not be filling.
It PO'ed a handful of customers, but what are you going to do.
No problems with steelies, well except lp72's. I would fill them, but others would not. There was rumor of a local kaboom of one a while back, so that ended that.