If a part is not showing (correctly) in the PLI, you have to add it to LPub3D's own library located in C:\Users\[Username]\AppData\Local\LPub3D Software\LPub3D\libraries.
There are 2 zip files there, the official library and an unofficial library. Just add your new parts to lpub3dldrawunf.zip and it should appear in the PLI.
There are 2 zip files there, the official library and an unofficial library. Just add your new parts to lpub3dldrawunf.zip and it should appear in the PLI.