Sorry to be the one who raises simple logic at this point, but hasn’t this chap already provided a refutable premise here? Without subjecting myself once again to this entire thread, I recollect that he says that these are not commercial aircraft, but rather, black (as in the paint, not simply the ops) aircraft. I’d suggest investing in a decent set of binoculars. Apart from time spent flying, I’ve spent my entire life as an ATC (and I’m old), and almost without exception, I can generally ID an aircraft producing a contrail by use of binos. However, even when I can’t make out the type, I CERTAINLY can see the paint. You’d be surprised. Try it. You'll find that you're almost always looking at commercial aircraft.
Dave