As far as I am aware, my user name never appears in the list of registered users at the bottom of the Forum Index page and I don't know the reason why. Could someone enlighten me?
It's because your profile is marked as hidden. If you go to your profile page, and at the bottom, under Preferences, there is an option 'Hide your online status', which you have set as 'yes'. If you want to appear at the bottom of the forum index, change it to 'no' and submit it.