MSOCS - Thanks. I'm really trying to smoke this story out.
You state: "It
[locating the labs stateside, I presume] isn't/wasn't a "condition" as far as I am aware."
The full story reads:
But even the current security regime is the result of a compromise by the U.S. In September 2014, JSFPO director Lt. Gen. Christopher Bogdan indicated that the foreign-owned laboratories would allow the operators more access to the system than they would otherwise have enjoyed.
That suggests that if building a U.S. lab was not a condition for buying the airplane, it was still the only way to have sovereign access to threat libraries. The Bogdan reference was from here...
Foreign F-35 Partners Allowed More Freedom to Customize Fighter Software - USNI News
... and if the JSFPO thought that USNI had it wrong they had lots of time to say so, and they didn't.