I have used LR 4 for years. Now I have downloaded LR classic ver 3.4 I tried to import the LR 4 catalog. I used File, Migrate and located the LR 4 catalog. I tried loading and got insupported catalog version. With a note to update catalog with Lightroom 6 or newer.
So I guess I cannot bring in my LR 4 catalog directly. So unless there is a work around I'm stuck.