It is likely you will rebuild on existing DCs to build your library. It’s important all parts are made unique when doing this, otherwise the part will use the first definition inserted.
Eneroth Deep Make Unique | SketchUp Extension Warehouse
This extension will assure all, including groups, are unique.
Method: First copy the DC then immediately right=click menu “deep make unique”
For DCs already having issues, place instance in a clean file, copy and deep make unique, right click and save to replace old definition.