1) Yes, I based my previous discussion on the only meaningful case - that there is no zener diode inside the relay. Just some form of schottky or switch diode.



2) The datasheet is not confusing. They are showing an image where you can see that pin 2 and 3 is the coil, and that pin 1 and 4 is the relay contact. And note 2 specifically say that the diode is optional, and for relays with the diode, pin 2 is + and pin 3 is -. Anytime you find a load with one pin defined + and one pin defined -, then you should supply the higher potential to the signal '+'. There is not anything ambiguous with the text. Nothing at all indicates that you should connect pin 2 to gnd. Pin 2 is expected to be fed a signal 5V higher than pin 3. Then it is up to you to define your ground reference. In this case, you seem to have defined GND at 0V, in which case GND should be on pin 3.


The reason for the polarity is the diode. So for a relay with an internal diode, you should have + on pin 2 and - on pin 3. For a relay without an internal diode, you may use any polarity.


Have you read the quality documentation the manufacturer have published? Do you really think that people who are selecting their relays are designing their circuits based on trial and error?


You are expected to blow relays if you connect pin 2 to ground and pin 3 to +5V. The datasheet specifically say that you should have +5V on pin 2, and follows up with "Correct coil polarity must be observed."

If you can afford it, you can take 10 more relays and connect pin 2 to GND and pin 3 to +5V. The expected result will be 10 more destroyed relays. That isn't really meaningful. It is way more meaningful to do what the datasheet explicitly says!