When can you tell if the "overlay" is active?

I’ve made a build of Legato, that removes some of the default apps and adds a few of my own. I make a custom image .spk file with all the components defaults except for my Legato version. I download it using Sierra’s fdt2.exe tool. All is well.
Now I want to test a SOTA download which consists of an .update file that again is the same version of Legato with some versions tweaked, just for testing. In other cases, the code is a little different, but in this case, the only thing changed is the version numbers. It updates fine and all is well.
Now I want to go back to my previous build using the .spk file. I download it, and it appears to program correctly, but when I look at the versions, it is like I didn’t program it. It remains to the later one. I have to program it with an earlier version that has significant code differences to get it to go back. Also, the update appears to not have used the overlay as the “app status” command yields the same order.
My understanding is that when you program with a .spk (with multiple .cwe’s in it) it is like a FOTA update that turns off the overlay, And when you use a .update file, it puts it in the overlay. In either case, why doesn’t my app(s) go back to the older version?
This is with WP76xx R8, Firmware.
and mostly, how do I know that the overlay is active or not?

Thanks

Hi @EvetsMostel, update through CWEs/SPKs is what we call a ‘firmware update’, because it updates whole partitions at a time.
Update through .update files are ‘software update’ because they update Legato in a more flexibly way, without touching the ‘golden’ legato image (read-only, mounted at /mnt/legato).

In the case of the software update, the overlay from /mnt/flash is used.

legato status should return the list of legato systems, along with the active system.

More info at http://legato.io/legato-docs/latest/conceptsUpdates.html