Does a sleeping bag comfort temperature rating increase with time?

I've had a mummy style sleeping bag, with 100% Dacron polyester fill, for the better part of 20 years. The comfort rating is -5 degrees F. I hadn't used it in approximately 10 years. When I used it earlier this year it got down to around 35 degrees F and I was extremely cold whereas I had never been cold at this temperature, or colder, in this bag before. I understand that as we age our physiology changes and we can get cold easier, however what I'm wondering is if it's possible for a sleeping bag to lose some of it's insulation benefits with time? I've found a lot of information regarding temperature ratings and how an individuals physiology needs to be taken into consideration, but I'm having a hard time finding any information on how the comfort rating of the bag itself can change with time.