I stored my entire record collection in a non-insulated shed for over ten years. They were tightly packed in Home Depot moving boxes that were 12.25 by 12.25 (width and height) and about 16" long. They fit albmums perfectly. Sadly, they no longer make that size. Anyway, I'm in a very humid climate and the temperature in that shed ranged from around 10 degrees F to 105 degrees F. When I pulled them out, some had those mold spots in your OP picture. I simply used my favorite cleaning method and the mold was gone. All of it. My cleaning method: Warm tap water Dawn detergent trimming paint brush (the flat ones that have a red or blue plastic handle). Sadly, my cassettes that were stored in the barn didn't fare as well. They shed so much mold on the head that they replicate open reel "tape shed". I have to figure out a way to clean them or throw them away... Fortunately only one box (out of seven) accidentally made it to the barn. Bottom line: I think that after you clean them they may be the VG+ you were promised.