It's probably safe to assume that they will no longer work. This source suggests that water-slide decals have shelf life of about 3 years. "After a few years the glue holding the decal onto the paper breaks down, fusing decal and paper together."

Because there is some variation between different decals from different manufacturers, they may last slightly shorter or longer than that in storage (like 3-5 years), but 30 years is probably too long. I think it's worth trying out one of the smaller decals just to be sure of whether it will work or not.

It's probably safe to assume that they will no longer work. This source source suggests that water-slide decals have shelf life of about 3 years. "After a few years the glue holding the decal onto the paper breaks down, fusing decal and paper together."

Because there is some variation between different decals from different manufacturers, they may last slightly shorter or longer than that in storage (like 3-5 years), but 30 years is probably too long. I think it's worth trying out one of the smaller decals just to be sure of whether it will work or not.