If there is any doubt that the tax return was filed, ask the claimant to submit copies
of both Form 1040 and proof of filing, such as a cancelled check, IRS receipt etc.
If evidence is not available, obtain the claimant's statement and request the evidence from the IRS via instructions provided in RS 01804.400.
NOTE: Exclude the earnings from the computation until it is established that a tax return
was filed.