I'm trying to get all of  but with any of the robots.txt options it'll only get
the contents of /th99/ and a few HTML files from /th99/z/

The directories below /th99/ are c, i, m, r, v, z. Each of those has one or
more subdirectories full of .jpg and .png images. So far no site downloader
I've tried has been able to get anything from below the directories directly
under /th99/

What's protecting them?! The site doesn't even have directory browsing
disabled.