You probably would have realized that some were slugs from the very beginning. I don't have a ton of experience, but in the last clutch my female laid, the slugs were obvious. They weren't the bright yellow or orange I've usually seen in photos, but they weren't bright white either. They almost had a translucent quality to them and they were much softer/pliable than the good ones.
As far as what's going wrong with them I don't know, but maybe when you added the extra water you added too much. Maybe you should do a quick change of the substrate to see if that will help.
One of my eggs is going bad too. Actually I think it's probably dead, but I still have hope. What I've done with it is just removed the mold by using a Listerine soaked Q-tip. Kathy Love mentions doing this in The Corn Snake Manual. You can also use Anti-fungal foot cream/powder to retard growth of molds, etc., or at least so I've heard.
Good luck!