It's surplus so hasn't been calibrated in a while... but that's easy enough to check (with a precise volume of water, for example).
And it's always agreed with the scales at USPS and FedEx.

More importantly - even if my scale is off, how could the weights be so different for two identical bottles, both labeled by NOS to weigh 14 lb 12 oz empty, 24 lb 12 oz full? work
One is 21+ lb and the other is barely 24.

I need to go out of town for the rest of the week, so I will take this up again when I get home.