Lucky you---and lucky flimsy that you found it! Somebody put a lot of time and love into creating that. As to the marks--I like the idea of repeating the design in the corners of the border. One of our quilt guild members submitted this to Fons and Porter several years ago and it does work on recent markings. I don't know if it will work on something that has been in place for years.
Combine three parts rubbing alcohol, one part water, and a squirt of CLEAR dish detergent to make a solution to remove pencil marks from fabric. Saturate a cotton ball with the solution and rub over the pencil marks. Leave it overnight and they should disappear.
Otherwise, it may be that you simply need to replace the border.