Found the new firmware shortly after posting - thanks. Tried it.
Still getting same result on ICCID/IMSI calls, i.e., no result.
I have still not gotten a valid location, but I did notice with the new firmware, the Sierra Windows Location Sensor now pops into “Initializing” state after plug-and-play detection of the device, where it previously always stayed in “Not Available”. Not ruling out a hardware / antenna issue on my end, as this seems “closer”.