What would be the purpose of attaching such a statement?  IRS is not going to send you a thank-you card for paying tax on the same income twice.  If you file an amended 1040, backing out the trust's income, then an attached explanation is needed.

So the decedent had a trust, but also an annuity with no beneficiary, so it went to her estate, and the estate paid tax on it?  The money is just sitting there, it was not distributed to heirs?  As I was just saying to a client yesterday, 90% of people with a living trust don't need one, and 90% of people who buy annuities, shouldn't. 

For tax preparers it's difficult to spot those annuities, since often they don't generate current income.  (Clients, however, may bring the annual statements, because they're as confused now about how they work as they were when they bought them.)