We bought a new house in February and had a similar situation with selling a game or two.
What's funny is that they said "we are not going to use this in the calculation since you qualify without it", but they still wanted the documentation.
Luckily I sold the pin to a friend who was willing to sign a bill of sale.
My wife and I also have a few side businesses that periodically spin off cash, so we had to document those deposits into our main account too.