1. I really think we've covered the circuit conditions about 10 billion times at this point.
The question has been asked 10 trillion times actually, but never answered.
There is more than one LM317 datasheet and typically more than one application schematic in each of them. And in dual rail systems additional protection is required, which IIRC isn't mentioned in those datasheets.
The parts were in no way abused, and the failures weren't even all under the same conditions (one failed in the unit the power supply was from, two failed on a dummy load).
The latter is closest to a reasonable argument you have made so far, albeit still no details of the test circuit.
2 other brands of the same part have both worked fine there.
Not an argument. They may have worked out of spec. This may have contributed to the failure of the original part.
Also, none of the devices ever reached 1.5A of current anyway (again, something I've covered thoroughly here), they died around 1A.
I gather that you have measured inrush current with a scope and aren't just making things up?
Like I've said over and over again here, NO ratings were even close to being pushed here.
Because "trust me bro".
Life would be much simpler if only people who are right were confident that they are right.
The "buy Chinese, buy twice" thing is dumb (frankly I find the constant Sinophobic echolalia around here absolutely moronic). The LM317K is out of production. The options were to buy these from Digikey or buy from random sellers on eBay/etc. I assumed Digikey would be the more reliable source for genuine parts than eBay etc, this didn't turn out to be the case but I think it was quite reasonable to make that assumption.
Ain't libel if it's true.
If DigiKey starts carrying transistor brands like ICS or Savantic, they will still be the garbage they are. And it looks like power ICs are similar story. And then of course lots of ICs with completely nonsense/misleading names, such as CMOS LDOs sold as 1117. Which kinda works most of the time, until it doesn't because you run into some important difference between these technologies.