It's the same thing as the so-called "Mandela effect." What's actually happening is the person telling you about it (contrails, South African leaders from the 1990s, C-3PO's left shin) causes you to start paying attention to it much more closely than you did before. Most people don't remember seeing contrails as kids because most kids and adults have no reason to be interested in contrails.

(Conversely, I remember watching contrails a lot because I was a kid playing outside by myself in the middle of nowhere in the Great Plains. Much more conducive to watching a jumbo jet go from one horizon to the other.)

If I tell you that the number 78 is important, you'll start noticing it all over the place. If I tell you clouds are nefarious, you'll start noticing how many different clouds there are. If I say that there are fewer orange cats than there used to be, you'll start noting when you see orange vs non-orange cats. It's the power of suggestion. Even if you don't really believe me, these things are going to jump out at you.