It's probably possible, though I'm unsure what it'd do to your JOB files. Since when you went to TA2020 it upgraded all JOB files to the current general survey version. The Trimble JOB converter is for upgrading files to a newer version and not saving files as an older version. It is possible if you switch to TA 2019 that your JOB files could not be opened without converting them to a JXL file which essentially makes data into coordinates and not bringing any raw data with it.