@daniel and community
--as followup -
using your tools, I've successfully gone back to original from old backups of mtd0, mtd1, mtd2, mtd3.
i've also successfully gone to the v1.1.1 installer and new ubi fs layout, with current (r25567) snapshot build running well.
the only glitch is seeming impossibility of going back to stck again, since ubifs cannot be detached from the production or recovery image. i await your next update to the installer,
thank you agian for these tools and your expertise