External calibrations have not already been applied to fluxes from the `sourceTable` parquet tables. You still need to read in the FGCM and jointcal calibrations and apply them. Furthermore, before applying the external calibs, you must "undo" the `LocalPhotoCalib` correction that has already been applied to the fluxes in `sourceTable`s (Slack thread here).
Yusra suggested that "somebody" should write an afterburner that applies the external calibs and inserts calibrated fluxes/positions into the tables. Could one of us be that "somebody"?