You CANNOT enter 2 EIN numbers on the Sch C so if you "upgraded" the sole prop to an LLC (a state designation only) then use the LLC EIN only going forward. If you have given a W-9 to anyone using the old EIN then give them an updated W-9 with the new EIN so the 1099 issued at the end of the year has the updated EIN. But even if someone issues one in the old EIN you can still enter it on the Sch C as both EIN numbers have been linked to your SS# anyway.
