Are there many images from the past showing that? If not, what's the difference these days?
Maybe so many more high-flying craft? Cameras not so good then?
Seriously, IDK. That's why I'm asking.
There is a fuckload of information on it, including a "Pre 1995 Contrail Archive" thread on metabunk (have not looked at it, don't know shit about it) and a bunch of controversy everywhere.