Thanks for telling me what to look for to edit posts.
Test was done to create and restore image by booting to the Acronis True Image WD Edition CD with the Western Digital My Book usb drive connected which is shown as drive E. The Win10 partition was shown as 1 drive letter later than where Win10 was originally installed. The backup image was created and then restored with no problem. The restored partition booted normally, and all drive letters were assigned the original drive letters that Windows created when the drive was initially partitioned.
The different drive letters appearing when booted to the Acronis True Image WD Edition boot media when an external usb drive is connected makes no difference, and this is another positive attribute of the program. The more I use the program the more I like and trust its reliability.