When using multiple rtl-sdrs at once, it is tricky to see which device ID belongs to which device. The cheapest units from China have all serial number set to “1”.
I have handwritten an unique letter to each of my rtl-sdr and then programmed custom product string:
rtl_eeprom -s jenda_F_-25
I hope this contains all information needed - owner, ID and PPM value. This can be easily parsed automatically and e.g. the signal can be automatically adjusted according to the PPM offset.