We will look at this, but unfortunately the system can only reject identical names automatically and, as far as I'm aware, there isn't anything we can add to it to alert us when things are similar.
We will speak to tech but if you do spot a new name that may cause confusion, do let us know asap - once someone has posted multiple times rather than just once or twice they may be less inclined to change.
From previous investigation it does seem to be coincidence rather than anything more sinister. Those who have joined us later may have had the experience of putting in a username and finding it's been taken (not as surprising as it might seem...'unique' nicknames often seem to be not as unique as we might think across the board, not just on GN or other websites) Hence people trying to think of a quick tweak so they can get on with posting.