Restore/recover Supersonic Matrix SC-91JB Android tablet
Playing around with "mount" and various commands, it looked like the /data file system was already mounted r/w. This left me with the option of trying to reload a "factory image".

The link you posted was informative and looks like a good resource, however I am a bit gun-shy about trying to load code that was not specific to the exact device in front of me, as I got burned on that once before (fortunately that one was resolved when the manufacturer finally made the correct stuff available).

I was finally able to get this one working without having to resort to trying a generic A10 image. I ended up using "echo -e 'boot-recovery\0' > /dev/block/nandf; sync", from within adb shell, connected a standard USB Windows keyboard from a PC, then issued "reboot" command still from within adb shell. Again I got an android on his back with a green triangle / exclamation point. I hit the Home button on the tablet and got into the recovery menu, and voila, the arrow keys on the keyboard actually worked to navigate the menu. I selected the option for wipe data / factory reset and used the Power button on the tablet as Enter, used the keyboard again to navigate the "are you sure" prompt, Power button again for Enter. The device showed that it was formatting /data and some other file system (I forget), then when it was done it went back to the recovery menu. I disconnected the USB keyboard and hit Power one more time to reboot, and this time we made it past the Android logo and back to a like-new out-of-box state! Back in business!

The concept of connecting a PC keyboard might be a breakthrough for anyone struggling with recovery on one of these tablets with no volume buttons, though I can't say it was entirely my idea. It briefly flashed through my mind at one point but I didn't actually try it until another post I read somewhere kicked me again. ;-)

p.s. I don't know if the exact sequence of connecting the keyboard etc was significant, but I figured I'd try to be specific just for the benefit of anyone reading this in the future.