Adding some info I learned.
A file ending with .cfg on a USB drive plugged into the router when it is powered up will in fact be copied from the USB drive into startup-config and onto flash: and nvram:
Once you have a startup-config loaded, the RESET button does nothing to default the router back to factory settings no matter what sequence of power on/reset or reset/power on or duration the button is held. It seems the only way to bypass the startup-config is via ROMMON confreg changes.