Apologies in advance for how complicated this is!
I'm a US citizen, my husband is not. Until January of 2021, he was a student and had an ITIN, and we elected several years ago to treat as a resident alien for tax purposes so we could file jointly. He finished his PhD, and his visa status changed, so in January he received an SSN, but all of his 2020 income was earned with the ITIN.
On his W-2 for 2020, there is no number in the "Employee's social security number" box 13a. Instead, it just has seven Xs, and says "XXXXXXX For" and that's it. I compared it to his W-2 from last year, which says only "Applied for" in box 13a. He had not applied for an SSN at that point; we have definitely filed with the ITIN every previous year.
We went to the local IRS office to have his ITIN and SSN tax records merged, but the representative we interacted with didn't seem to know what we were talking about, and told us if we filed with the SSN, the file would "automatically update." Since the IRS webste is very clear that it's our responsibility to ask to have the numbers associated with one another, that doesn't seem to be true, so we're left with having to send the IRS a letter as explained here.
Given all of the above, what do we use to file this year? Do we use the ITIN, since he didn't have the SSN until this January? Or are we obligated to use the SSN now that we have it, even though the IRS won't have merged his records before we have to file?
