Importing catalog didn't include photos on external drive

I created a new catalog in order to import my old one to hopefully fix some seemingly broken links I had. Though this seemed to work, I ran into another problem.

I have catalog with 80,000 photos. 17,000 are on my local hard drive, and the rest on an external. When I created a new catalog and imported my old catalog, it only imported the files that were local—around 17,000. There is no mention of my external drive (and it is plugged in and accessible from the original catalog).

Does anyone know what's happening here?