You must do this reset procedure first time, even you start from sd-card. (if you update android version, you must press again first time)
Not necessary if installing to internal, and of course, not possible if there is no functional Reset Button
Can you expand just a bit on how you were able to get it to boot into the SD/USB to install LibreElec, without using the reset?
I chose the zip file (nand installation) from an earlier build and put the files onto an SD card.
Then I put an empty zip file called dummy.zip on the same sdcard and chose that as the update source from the Android Update program.
Once LE booted on the box I upgraded using the .gz file and device tree (actually not sure if I changed dtb.img) in the .update folder of Kodi via SSH
I think the stock recovery had no menu and that is why it never appeared to boot to it.
Once it had something to do, recovery was in fact present, and installed the update
MAKE SURE YOU BACKUP THE ORIGINAL DTB FILE FROM ANDROID as, once LE is installed internally, the only way to recovery is with Android dtb.img and recovery.img on SD card and issue reboot recovery via SSH (or similar)
Is it possible to flash another Android of other boxes
Be careful with that one