Copyright status of Cesk Zadeja's pieces

[asdf]

I came across several of Cesk Zadeja's pieces on IMSLP; this surprised me, because he died in 1997. Not only are the pieces on IMSLP, but they're also under some very free licenses. Have Zadeja's heirs freed all his works, or only the ones currently on IMSLP?

[Carolus]

I believe they have only allowed the ones here. It could be a case that it's taking them time to prepare material also.