Ok, I'm guessing now but I think we're using a similar size paper. I also use copics (sketch) and a big part of them is over 10 years old. Still pretty fine, except for those which dried out because the cap went off during transportation. Bad luck I guess.
Maybe the difference is in that you're working bigger than I am. Or you have more patience. I must say, your artworks really inspire me to try harder and learn more because you're using the same medium I love and have really magnificent results. I want to reach that as well
Thanks for sharing the photos!
Definitely need a different white pen. The edding I currently have is just not reliable. It either does not release anything at all or splashed out a gigantic blob or white and ruins everything.