Entries in Global List variable must be unique?

I have a global list variable in which each entry specifies an icon to be used depending upon another global variable which holds a 0-based, numeric state value. I wanted to be able to use the same icon for more than one state.But that doesn't seem to work as the list ends up incomplete.

It seems to me that in a list, the most important thing is the entry/offset, not the text shown at that offset. Indeed, when I access the global list I am accessing it via index, not by text value.

Why is this?