Good news! After messing with photorec, untrunc, various fun ffmpeg incantations, etc... I found a GUI app, "Disk Drill", that has 'Advanced Camera Recovery' and pulled the files right back from the dead.
I was _close_ with the open source utilities, but the app finished it off
Did not plan on spending 6 hours yesterday and 4 (and counting) today trying to recover some Sony MP4s I fat-fingered out of existence.