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I'm pretty sure that if he is the only one buying the house and it will be on his name only, he doesnt have to worry about his wife's credit.
If they were doing a joint purchse, then it might be an issue. Still a 30 day late is not that big of a deal. You can explain it to the underwriters that it was an oversight. He will also have to explain the reason of his short sale.
If his scores are good, he doesnt have major deragatories (collections etc) and he has the funds, I dont forsee a problem.
The wife may be able to ask for a GW adjustment to her payment history, since it was indeed an oversight and a mistake... I once paid the wrong amount, my aunt had died that day, and I paid 82 dollars less than what I was supposed to. My lender didn't care because the escrow had plenty to cover my accidental shortage. Maybe the wife can contact her mortgage provider? Either way, her history won't affect his ability to get the mortgage.
it wont' matter. They will probably pull her credit just to make sure he's not on a house that he owns w/ her or anything, but since he's not on the loan and she's not on his loan, it is nothing to sweat about.