Yup, letters are used quite often when a lender/customer needs information quicker than the information can update on a credit report or information that can "override" a credit report for lack of a better term.
I can think of 2 personal examples: Back in 2015 when my report was dirty and I went for a car loan the dealership was having trouble securing financing for me with the 619 score they pulled. I had a late payment showing on my CR from a month or two prior on my mortgage that was there in error. This was before I found this forum and ever looked at my credit reports, so I didn't know it was there. I called up the mortgage company and they faxed a letter to the dealership stating that the account wasn't late and the dealership financing department used that to get me approved. Second, I've had a high previously reported balance on my Citi card and have missed paying it off to $0 by the time the statement cut. I've contacted Citi asking for an off-cycle reporting to get the $0 reported (which they won't do) and they've said they would send a letter to my LO stating that the account was paid off which would allow them to make a DTI revision on their end when looking into a potential mortgage.
