That is a very comprehensive and useful analysis. Thank you for this contribution. I too had noticed that the visible LED was not a reliable indication of operation (Directly connecting to Optical Pulse Counter with RPi? - #59 by Robert.Wall and First try with EmonPi - Pulsecount stuck at 1 - #16 by Robert.Wall)
I’d add - for the benefit of anyone less experienced in these matters who is reading this, that those ‘resistances’ you’ve calculated are probably non-linear, and probably vary quite a lot from device to device. You also found that between the ‘on’ and the ‘off’ states, there is a more or less linear region where the output is proportional to the light intensity. So there are not two distinct output states as the manufacturer’s description seems to imply, but rather a ‘low’ state that corresponds to very low light levels, a ‘transition’ state where the output is some function of the light level, and a ‘high’ state where the sensor is saturated.
My take-away point from all of this is, if the sensor can see any ambient light at all, ignore the LED on the back and check the output voltage for correct operation.