Just an example here.
I had a joint car loan with my ex husband that he was late on a couple of times. I disputed it as not late, ONLY because I thought it was the loan for my car not his (we had 2 loans with the same bank). They validated and the disputed stated that I should call them. I went ahead and when they told me it was for his car I was like "oh bummer, and there's NOTHING you can do to help me?" and she said "sorry we can't remove accurrate information" well, 2 days later it was off my reports. Sometimes "no" means "only if no one sees me do it".
An even BETTER example is just recently. Early last year I had a dental bill go to judgment because I lost their letter with their number on it. I tried to look them up in the Yellow Pages but their business name gave no results (local CA, it turns out they listed it under an accronym). I found the slip and called 2 days after the deadline but the damage was done, but I set up payments and paid it off asap. A few months ago after finding this forum I decided to write a letter to them explaining everything and asking for them to remove the collection account so that I might be able to get the judgment removed. Over 3 months I sent 3 letters, no response whatsoever. I finally just called them and asked if they had received it and they said yes but that they never removed accounts and if there were EVER exceptions that only the owner could make them. I sent my letter to his attention directly and 3 weeks later holy crap it was gone from 2 of the 3 (TU is agonizingly slow to update).
The moral of the story is that it CAN happen, but it WILL take time, and usually several attempts. When re-sending, change up the letter and try other addresses, other departments, or google the creditor to see if you can find a manager's name or something. All it costs is a stamp. Good luck to you.