Steve Davies' recent book "Red Eagles" has lots of information on the Constant Peg program in which the US operated a number of MiGs under cover designations from YF-112 upwards. He also has full details of the Bond MiG-23 crash.

Of course, you can believe what you like, but Steve is a great author with impeccable sources.

The most likely explanation for the missing F-19 is that Northrop were due to get F-19 for the Tigershark but requested and received F-20 so it wasn't the last of the "teen fighters" but the first of a new generation. The resulting gap proved very handy for disinformation. Given that the F-117 and A-12 both received non-standard designations to help conceal them it would be an act of monumental idiocy to assign F-19 to such a supposedly secret program as you describe.

Personally I believe 100% in John Lear when it comes to the Northrop F19.

And there is ZERO evidence for it. A testors model, is not evidence of anything.

Not only that, but some things he has said about it are actually rather wrong.