Thanks for the reply, Lugh.

For Windows 7 MS Office 2010 the regedit location is:-
HKEY_CURRENT_USER\Software\Microsoft\Office\14.0\W ord\File MRU

On trying to delete all of the entries (following a regedit backup), not surprisingly the "Default" value cannot be deleted.
I deleted the rest, then restarted word and saved a couple of blank documents.
Closing Word, then hovering over it in the Start Menu did exactly as before (i.e. nothing!).
All the old "Recents" available from Word's File/Recent had gone; just the two new ones were present.
So it looks like the "hovering" Recents are not the same as the File/Recent Recents.

Any more ideas???