Certain colors are fugitive (prone to fading), such as Opera Rose, no matter the brand. I wouldn’t think that Jane used any of those, without noting that they were fugitive, though.
Personally, I haven’t had any problems with fading in my watercolors of any brand. The environment can make a difference even if the colors are in a closed book. The paper can also make a difference. I haven’t used Canson XL but I’ve heard mixed reviews and fading has been mentioned, so it could be your culprit.