Ok, so the issue that I saw may only be related to more than one Powerwall. One had the import/export counter left as-is and the other had the counters reset to zero.Only one PW and plausible import / export data. That for the battery says:
energy_exported: 5958950
energy_imported: 6990200
which is consistent with the overall 85% efficiency I calculated a year or two ago (my battery has a relatively easy life particularly during the summer half of the year when it rarely gets below 50% charge).