Thanks for the feedback and for writing up your experience @johnbanks.
It is now possible to restore via USB sd card reader import method, described here: Backup module usb-import.sh script (beta)
It’s partly intended to get around the issue of needing to store large backups on the same SD card as the rest of the data, and also helps with restoring from a corrupted disk that wont boot to create an export archive. I had the same issue with a power cut the other week. Using fsck to fix the disc prior to import may be needed…