Check out this video from What If Science to find out what would have happened, if you actually ate mold.
Warning, this content will gross you out!
The products (especially those that have been opened) – even if they have just a small hole in them, need to be stored properly at the right temperature and need to be used within the proper “use in X days” time frame that is suggested on the packaging.
Otherwise, mold may form on these products.
Do note – That is NOT the “Best By” date.
Fresco Control can help you with keeping track of that, as it warns you how long the product is good for after it had been opened, as well as warns you if the temperature exceeds or is lower than the suggested temperature for the product.