There was a recnet posting about "jail breaking" your slabbed cards. This reminded me of my situation late last year when I opened up one of my card storage cases dedacated to slabbed only cards. So, like many of us we go through the highs and lows of collecting. I generally only collect during the winter months when I spend more time inside and this past winter was no different.
I started out by looking at some of my old collections to get the juices following and then I planned on what I wanted to collect this time. I made a decision on making a serious push on my prized Mike Schmidt collection. I have an extensive Excel spreadshhet of which I keep all my cards of him listed as well as list ones that I want to obtain. So, as I said above I opened one of my cases and started looking throught the slabs. I then suddenely noticed that a hand full of cards lookied slightly different. I could see what appeared to be "fuzz" inside the slabs covering some of the card inside. After going through the whole case, about 60 slabes, I pulled two dozens slabbed cards with this "fuzz" inside. I started to "Google" what It may be, but my gut kinda knew. It was MOLD.
I went to my LCD and asked him if he knew of any issues like this. Since most of my slabbed cards were purchased from him i figured he would know. Notta, nothing, dead end. So I did more "Googling" and found some info and after some intense research, I fould that some of the older paper stock that Topps and other card manufactures used were not of top quality. As well as improper handling & storage techniques over the years, and the ever so slight possibility that the slabs were opened and the cards inside were swapped out and improperly resealed.
After opening all the slabs, I ended up trashing 15 prized cards and I was able to save the remaing ones using the "baking soda technique". Thankfully most of the mold was contained on the outter edges of the cards which made it easy to clean up. I also found that using Desiccant packs inside those plastic sealed cases helps out alot. It helps to obsorb the air that gets trapped inside the case, just make sure you change them out every 4-6 months.
I've since replaced those 15 cards including my Schmidt rookie. and the remaining ones that I cleaned are holding strong with no signs of any mold returning.