I've learned a couple of other things during this process.
After the first extraction "succeeded," I found that there was a major discrepancy in the number of files on the volume as reported by icon Information versus the number of files in the archive as reported by lha. I ran lha with "-t" option, to only extract new files, and found the Workbench as a whole came to a stop at some point in the process, usually around the same file.
I tested the archive with lha and 7-zip and found no errors. Then I ran PFSDoctor to find that it had to repair two directories. Afterward an entire drawer was missing from the drive. I ran lha with "-t" again and everything finished successfully.
But I found that I still had a number of files missing (about 126 files,) and the byte count was off. I opened the archive with 7-Zip on a non-OS-specific Intel-based machine and fired up DOpus on the Amiga and ran "Get Sizes" on all of the contents. I compared byte and file counts on both to find that all but a single file had extracted. Effing weird, but I now none-the-less have a working PFS3 volume.
Now, something else I determined which I think will be of interest to anyone else doing this process with a USB flash drive. During this process I was running MiamiDX and a USB Ethernet device. I have seen on Windows machines where the driver crashes and the USB Ethernet device locks up the entire network, and that's exactly what happened in my case -- the entire network became non-responsive. (I didn't bother to run any packet capturing on the network since the switches indicated no traffic what-so-ever.)
The USB flash drive was still running full-tilt. I brought up MiamiDX and put it offline then brought up Trident and disabled the Ethernet device, which put everything back to rights. (This actually happened during a previous extraction, as well, and I was able to just power-cycle the device as well.) Returning the Ethernet device back to service is easy: power-cycle its parent hub or reboot the machine.
Hope this information is interesting or useful to someone.