Are they supposed to be stored or treated in any special way?
I'm sure a lot on how well they last depends on the environment where you store them and what the mold is actually made out of. I buy other molds from a company called
Hirst Arts and he recommends the following for storing the molds long term.
Q: How long do the molds last, and what is the best way to clean and store them?
A: As long as you use gypsum products (such as plaster, hydrocal or dental plaster) the molds will last for years and hundreds of casts. I've never had a mold wear out yet and I've used some as long as 3 years.
Usually the molds don't need to be cleaned. If mixed properly, the plaster will pop out of the mold leaving no residue. Sometimes you will have plaster on the face of the mold which you can simply rub off with the palm of your hand. If you do need to clean them (maybe after 10-15 casts) use soap and water. An old toothbrush works well to get down into the mold cavities. Do not clean them with paint thinner or solvents! They will soften or dissolve the mold.
If you're going to store the molds, give them a light coat of talcum powder (baby powder) and store them laying flat. If stored on their side for several months they may tend to warp.
Bruce's molds, Hirst Arts' molds, are made of a blue colored material, while the molds you used are black in color and of a different texture, so I'm pretty sure they're of different make ups of similar materials, so I would say Bruce's method should work for them as well.
Personally I don't do anything to help store my molds other than to keep Bruce's molds in the house in A/C, but I check on them from time to make sure they're not sticking together. The Woodland Scenic's molds just get dumped in a box or paper bag and usually end up in the garage, so I'm pretty sure they're more hardy than Bruce's but I'd say if you dust them with baby powder they should be fine.
Oh and your mine looks good.