What is the difference between unserviceable, unusable, and not maintained?

Here are some NOTAMS for a recent flight I was planning:

LXY 03/002 LXY NAV NDB U/S 2203081935-PERM

CRS 02/008 CRS NAV NDB UNUSABLE 2202141320-2206142111EST

ANB 05/580 SJI NAV VOR NOT MNT 2205201953-2205232000EST


We all see these kinds of NOTAMS all the time. In each case, I would consider each NAVAID to be unfit for navigational planning or flight use purposes, meaning that I now consider all of them out of service and not to be used. But is there any actual semantic difference between the qualifier in these three cases? Or do they all just mean, "it's not working, don't use it!"? If so, why are three separate qualifiers used when UNUSABLE would be sufficient?