You're right, importing the folder where the clips are locally stored won't give the info you're looking for.
I've done a quick check, and it appears that the titles of all audio pack clips available from the App Manager are
already loaded in PD19s Sound Clips and Background and Music libraries. The problem is that if you download a full pack from the App Manager, PD doesn't update the Download entry in those libraries to reflect the content that's now on your PC.
Instead of using the App Manager, if you download the clips directly from either of PD's sound libraries, it does keep track of them and you'll be able to see all available clips by sorting by Download status and genre, so that's what I'd recommend doing.
From what I can see, there's absolutely no point in using App Manager to download these audio clips since PD apparently has no way of displaying the downloaded content. It sure seems like an oversight or a bug.