Dear Samuel,
For this question we defer to IRS regulations. The formed unincorporated entity would have a tax id number. A new number must be applied for when the company now incorporates. You are correct, that the incorporatred intity now is the legitimate entity.
However, it is possible for the corporation and the unincorporated to co-exist and continue to operate seperately.
It would have to be shown that the INC was an alterego of the unincorporated organization, which it is not.
YOUR PAYMENT AND BONUS IF ANY MAY BE TAX DEDUCTIBLE

Edward M. Johnson