About the md5sum's of the image files . . . .
- Each image file contains (in /etc/shadow) a machine serial number based password for the user 'root'. The md5sum's will differ if the images are from machines with different serial numbers.
- Each image file contains files with three timestamps, one of which is the "last accessed" (atime) field. Even if the images are from the same machine with the same serial number, if the last time any of the files where accessed are different, the md5sums will be different.
- The non-windows file system (the ones listed here) have meta-data super blocks, each with a "last mount time" - which gets written to even when the media is mounted "read-only". This will also cause the md5sums to differ.
Instead of comparing image md5sums -
Mount each of the images;
Copy out ("cat") the contents of <mount-point>/etc/version.txt and <mount-point>/etc/prettyversion.txt and post those contents.
It those exact file names are not present in an image, browse around in <mount-point>/etc until you find something similar.
The <mount-point>/etc/version.txt will have a software "build code" in it and a software build date.
It would be nice to see those.