You have to make sure a call to SetLibraryList or AddtoLibraryList is done as soon as possible after the application starts. The application Open event would be ideal.
The first time an object is referenced, the entire pbd/pbl is loaded into memory and it adds every object to a memory location index. This makes instantiation of other objects much faster.
Adding new libraries to the library list after the index has a lot of entries in it can cause issues. In particular, it prevents an object of the same name in the new library from replacing one in the base library list. Even if the new library is at the top of the library list, it will not update the index.