Default for Global Variable Not Working

I am a newbie. So pardon me if I am just dumb...

I have created a global list variable and populated it with the names of 3 font icons I want to show based upon a computed numeric value. This all works fine as long as the value computed is within the range 0-2. (BTW - I could not find documentation saying if these lists are 0-based or 1-based and had to find out empirically).

But if I get say, 60, sent I am always being returned I don't get my specified default value. Based on the limited documentation shown here, I am using the following to compute the icon name:

$gv(icons, adb, #)$

where # is the computed value. If # is 0, 1, or 2 I get the right item from the list. However, anything other than these three values always returns the last item in the list. So if # ends up being 60 or "foo", the result is always the last item in the list.

The documentation says that the second parameter is "An optional default to return if global is not found". Perhaps this means only what to return if no global called "icons" exists. But it seems that for a list variable, an list index out of bounds is semantically the same thing. Is this NOT the case?