I had updated the firmware to 1.0F, so either type would have worked. The upgrade was done not for LTH, though it's listed as an improvement, but for "Writing performance and reliability improvements," per Sony website.
The LTH designation would probably be obvious, so the discs I bought likely weren't. And from another post in this thread, it seems as if this technology is rather new. The discs I bought were manufactured in 2006.
In fact, there's no way the discs are LTH. The latest firmware only allows the "reading of LTH BD Media."