I wanted to update this with the solution.

I bench tested the original (date code 2001) purge valve every which way possible (solenoid resistance, Foxwell active testing, confirming the valve was opening and closing), and it seemed perfect.

But I had read other cases on other BMW forums about this situation and it seemed that the smart money was on replacing with only a Genuine BMW part. I went with that, 13-90-1-433-603 , and the code never came back.

Maybe an aftermarket part for 1/3 the price would have worked, but considering already existing uncertainty about a bench-tested part still throwing a code, I did not want to take a chance.

I also found some weird non-synchronization with the BMW DME-44 code, OBD2 P0444 code, and SES light. The BMW code would show up with neither the OBD2 code nor the SES light. And then the OBD2 code would come along to join the BMW 44 code, but still no SES light. And then eventually the SES light would come on as well. That was a surprise to me. I expected them to all be there or none of them.

Passed CA smog earlier today.

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2001 X5 3.0i, 203k miles, AT, owned since 2014