@Sam2717 wrote:
They did change us to spouses in their system
At least you are correct going forward.
As far as the imputed income from July through the date of the correction, it is correctible. It's a matter of whether they want to do the extra work.
(Specifically, they probably can't correct the federal tax withholding, whatever was withheld was withheld. Box 2 on your W-2. But they can correct your box 1 taxable wages, and if the wages are lower, the excess withholding would result in a larger than normal tax refund. They would also have to reduce your box 3 and 5 wages subject to medicare and social security tax, then reduce the box 3 and 5 withholding, and that would be refunded to you in cash rather than getting it back on your tax return. It's uncommon but it's doable.)
It's mostly internal bookkeeping, but it's not a common issue and they might not know how to do it, or they might not want to put in the work. That would leave you with correcting it via your tax return, for which I recommend hiring a pro to help, because you could get questioned by the IRS.
