Marriage, gender, and US income tax

Factual Questions
1

Inspired by this thread:

Does the IRS do any kind of verification that a couple is in fact mixed-gender? I mean, if Jo Smith and Pat Jones file as married-filing-jointly, does the IRS do any cross-checking to see that both Jo and Pat have ‘M’ on their birth certificates? Can’t go just by name - I knew a girl named Michael (as well as actress Michael Learned) and there are quite a lot of other names that are used for either gender.

Obviously if they do twig to the fact that Jo and Pat have similar plumbing, they could nail them on tax fraud.

Similarly with a couple where one member is transgendered. Does the IRS recognize a pre-op trans as the old sex or the new one?

All this presupposes that the couple is legally married (vs civil union) in their state of residence; I know those laws vary widely.

2

I doubt it. I also doubt that the IRS has any of knowing whether I’m really married when I file a joint return. My marriage license is filed in my town so Massachusetts probably doesn’t even know for state income tax purposes.

I’m sure some audits ask for proof of marriage. Even then, unless the sex of each partner is on the marriage certificate, even an audit wouldn’t catch the marriage of Chris and Dana unless both of them went to the audit.

[opinion] States determine whether a couple is married. The IRS should honor the state’s determination of marriage. [/opinion]