Agreed.
What is more reasonable, smoking out a source that is vouched for, or Romney simply providing a copy of a form he swears was filed, completed, and paid yearly? I mean, I guarantee he has a guy who's job it is to go grab this stuff out of a file folder, make copies of it, and mail it out as necessary.
No one is going to tackle the source when the other is so easy to prove/disprove.