SFI is the standard in safety equipment and they recommend that seat belts be replaced or recertified every two years. At the Santa maria national, this rule will be enforced so the month will matter. Please check your belts so you are in compliance at that event.
If you read the article it is well written and makes a lot of sense. However it specifically talks about damage done to exposed seat belts to direct UV and Indirect sun rays. I do not know of anyone whose car sits outside or even has seat belts constantly being bombarded by UV rays. I think you should be extremely concerned with your passenger cars a specially those with kids in car seats who have crashes then. My observation no safety expert so bomb away!