1. Yes, write 100 times: there is no /etc/fstab used in LE.
With UUIDs this should work. Only with a second copy attached the same time you don't know which is mounted.
2. A long we don't know why the LE image is not accepted this cannot be corrected. Use what is working.
I've created two additional test images, please test on a spare stick if you see the syslinux boot messages.