But I agree there's more than one way to view ownership and I can see your point, even if I don't think I agree so long as the UK can truly operate it in every way, including software that might need adapting (like how I might bend my fork's prong back into shape, or out of shape for adaptations)
https://www.czdefence.com/article/europeanisation-of-the-f-3...: “The F-35's manufacturer, Lockheed Martin, states that currently around 25% of the F-35's components are manufactured in Europe.”
That doesn’t say the USA cannot make every part, but I think it’s likely they will have trouble producing some of them.
For example, https://simpleflying.com/how-many-international-parts-us-f-3... states the F35 has Martin Baker ejection seats and the F35B has Rolls-Royce engines.
“On 27 May 2006, President George W. Bush and Prime Minister Tony Blair announced that "Both governments agree that the UK will have the ability to successfully operate, upgrade, employ, and maintain the Joint Strike Fighter such that the UK retains operational sovereignty over the aircraft." In December 2006, an agreement was signed which met the UK's demands for further participation, i.e., access to software source code and operational sovereignty. The agreement allows "an unbroken British chain of command" for operation of the aircraft.”