When you have shared cells many levels used within are not shown as used in the level list.

When you sort your levels for used ones levels in shared cells are not listed.

You can switch off levels ""Off by element" but you will not be able to find the level again when you sort the level display for "Used" or Filter for used for that matter.

In the Properties you are not able to identify what elements the cell consists of and the levels that are used within.

This should be changed to show up somewhat like normal cells. There you can see the cell and all the containing elements and the levels that they reside on.