There are also different versions that respond differently.
VERFW:00090.19 Standalone OG 7.2 reports 2 strings + totals
VERFW:00090.19 Parallel OG 7.2 reports only 1 string per inverter + totals
VERFW:00069.06 Standalone OG 7.2 also only reports 1 of the 2 strings + total
So provided you have the meta data about which inverters / versions behave which ways you can infer the second string, but the sample rate of the data then becomes an issue if you want accurate readings.
All in all, the firmware for these things is bad. Pretty much no QA done on it.
Dave