If the records were worth something more than the paper they're printed on, I might agree with you. However, considering vis really only applies while the guys has the light in the tank, it's sort of a moot point. If it passes vis at the time of sticker, what happened before that is also moot. If it shouldn't have passed vis, that's a much more important issue than what the sticker says. What happens to the tank after that is out of the inspectors control, so the sticker really is completely meaningless.
Regardless, backdating a sticker so that it aligns with the hydro date is not a problem. Since those records don't actually mean anything anyway, you're getting your panties in a twist over nothing. Quite literally, you're getting upset over something that has absolutely zero meaning whatsoever. Slap a generic sticker on there and be done with it.
Are tank inspections important? Absolutely. Yearly? Not according to the DOT who has actual force of law behind them. In fact, hydro is the only legal issue at play here. Is getting bent out of shape over what a sticker says important? Not in the least. You're getting your blood pressure up over something you have absolutely zero control over.
If you're so bent out of shape over it, skip the vis, get the hydro 6 months early and sleep well at night knowing that you've fought some good fight against something that only you consider an issue. You're the one diving your tank, not me. Since it's your tank, pull the sticker off before its time runs out at the time of hydro. Man, think of how many kittens and puppies you just saved!!!!