There must be something different in the way some products are being used from person to person. That is the only explanation as to why they work for the majority, but not for a few. I can only say I've been quilting for years, and my Mom and Grandma before me, and yet none of the quilts that had blue markers used on them have had the marks return. I often wonder what the difference was. Some have said it has to do with ironing, which could be true. Also I've heard all fabrics must be prewashed, which is not true by me (I don't prewash, only test). I've heard some people don't wash their quilt, but 'spritz' the marks with water and expect that to remove all marks forever. Spritzing only pushes the markings deeper into the batting to return at some point. It does not REMOVE them from the quilt.
You see, I think there are so many variables involved when people have problems - and stories get told. But, it's so hard to say what caused it one time and not another, as we don't know what anyone else really did - and they may not know themselves. I only know I don't prewash. I never touch marks with an iron or TX summer heat. I mark heavily. I do not 'spritz', I WASH. And I have no problems. That, I can say, has always worked for me :)
Hope this helps someone :)
Debbie in Austin