You're right. Only one could claim it.
It's like if a divorced couple has a kid to claim. Only one parent would be entitled to the claim. A failsafe for that situation has been in use for a while. The kid's SSN. It must be entered onto the tax forms in order to take the deduction/credit.
If both parents tried to claim the child, whoever claimed them first would get the deduction. When the second parent files, IRS will kick back the return. If there was a reason the second parent would be entitled to the return, like if it was in the divorce decree, then the second parent would be able to take legal action to get the tax deduction/credit. But, that's way beyond my level. I merely enter numbers into the forms for people.
Perhaps, in the future, now that more and more hybrids are being sold, there may come a time when we'll have to enter the VIN to take the deduction/credit. But for now, it's taken on faith.
And speaking of the future, who knows if the tax breaks will last long! Maybe in a year or two, the tax break for hybrid cars will disappear!
