Form 5500 - Which Version to Use for Prior Filing

We have a strange situation.  We prepared a 2018 delinquent Form 5500 for a large plan in December 2021 and the auditors assured us the opinion would be finalized and sent by 12/31/21 but they only sent in February 2022.

The issue is the version of F5500.  We had prepared it on the 2020 version which was the latest version available at the time.  Now the 2021 version is available, do we need to reenter data onto the 2021 version and submit or is it fine to file on the 2020 version?  If anyone can share their experience or insight that would be much appreciated.

The DOL Form Selector Tool should tell you. Most of the forms will likely need the 2021 version, with some exceptions. 

 https://www.askebsa.dol.gov/FormSelector/ 

I know some e-filing software tools allow you to download the data electronically (so, download the 2018 data) and then upload the data electronically again (into 2021) so hopefully that saves you a step for typing it up?