Why does the reported frequencies and the STATA frequencies of SSMC not match up?

Here is a screenshot from STATA side by side with the case count frequencies of IPUMS USA

And here is my data extract. I do not believe I have done anything out of the ordinary. Thank you for any help you can give.

The reason why your frequencies are so much higher is due to the fact that SSMC is a household level variable. In order to get the appropriate count of number of household, you will need to limit your tabulation to one member of that household. This can be done with the following:

tab ssmc year if pernum == 1

One note about the SSMC counts you see on the code tabs is that counts for those with a code of “0: Households without a same-sex married couple” include vacant households (cases where VACANCY > 0), so even when you tabulate SSMC using PERNUM == 1, the codes will still not be a perfect match.