I would like to see you get straightened out with using internet sites to identify planes you can see in the sky.
After you are satisfied that they are all accounted for, or nearly so, then we can get on to how and why contrails form, and how and why they dissipate, or not.
After you are comfortable with the behaviour of water (all 3 states) in the upper troposphere, we can move onto air traffic patterns and the way the density has changed over time.
So, relax. You have come to the right place for the information you seek. I'm sorry and I apologise if you feel like you are being mugged (although I'm not responsible for it). You see, we all have specialties, and you are jumping all over them. Pick one topic and stick to that until we've cleared it up for you.
You are doing well, and thanks for persisting.