A few years back I took in a pair of 30's to get replaced or recertified and OPD valves installed.
I was discussing the situation with the tech there, an "older" fellow and well seasoned in his work. He could sell me new ones or recertify my bottles.
He was telling me that the older tanks/bottles were of better quality and thicker steel than today's bottles. He demonstrated by offering me two empty bottles to pick up, my old one from 81 and a new one. I did so and could feel a very distinct difference in weight. He said I was better off keeping an old one fitted with an OPD, rather than an all new bottle, provided the old one is in good physical condition.
I don't care about a few pounds of weight, it makes no difference to me whatsoever. I'd rather have a stronger bottle in the event of a serious collision or rollover situation.
To me it makes sense, as everything from yesteryear was built bigger better stronger and meant to last. Today's standard is cheaper thinner lighter weaker and built in obsolescence. All for the sake of saving a penny.
I chose to keep my bottles and have them updated to OPD.
Almost every time I get any bottle filled, they check the dates on them. Very seldom I will get a nozzle jockey who just fills them without looking at the dates.