We picked up a new client this year who already had their 2019 return done for their business. They weren't happy with their preparer, so they came to us to prepare their personal returns and double-check their business return.

According to their EIN letter from the IRS (dated 2009), the EIN was issued for a single-member LLC.

The business filed Form 1065 as a two-person partnership for 2018 & 2019. (The son joined his father in the business. The father filed Schedule C for 2017 and earlier years.)

The business should have applied for a new EIN when they made the switch from single-member to multi-member LLC.  We'll apply for a new EIN for them now.

But should we do with the two Forms 1065 for 2018 & 2019? In those years, the business was actually a partnership between father and son that filed a partnership return, but used a "disregarded" EIN.

Suggestions?