You don't have 3 Addon Managers installed, you have 3 uninstallers for it. The Control Panel Add/Remove Programs doesn't indicate what you have installed, it indicates the uninstallers you can launch, it's not the same thing...
There always only one copy of the Addon Manager installed in FSX but you might end up with multiple uninstallers in the Control Panel, if you manually removed some files, without running the uninstaller from the control panel, or manually removed the uninstaller, or something has gone wrong with your registry like a registry cleaner utility that has being confused.
If you want to have only one copy, which doesn't make any difference other than cosmetic issues, remove them all 3, and reinstall.
