How do you know moldy cheese is not spoiled?
Given the salt level, and level of "good" mold, not much can go wrong, and there is a very low risk of anything dangerous happening. It's probably going to dry out before it spoils.  Any storage that might happen is probably due to improper storage.  This is one case where smell and visual tests can help you determine spoilage. If you smell the aroma of ammonia, you probably have a problem.  If you see fuzzy mold, or mold that is off color, that is a good sign that there is some spoilage.  Any slimy cheeses should also be discarded.  Finally, if there are no obvious signs (or you see subtle signs) you can go ahead and taste it.  This is not normally something I would recommend, but again, with blue cheeses, there is a very low chance that something harmful is growing.  If it tastes off, that's not a good sign.