The information about who is using a document comes from the Office registration settings. I can't say for certain that this is your problem just that I have seen Office applications with invalid in many places with invalid information. My bet is somebody else was editing the document, but just had incorrect name/initials in Office.
On my network I resolved this by creating a login script that reset the Office username at logon time. This is tested for Office 2010, the username/initials might be somewhere in the registry for 2007. The same idea should apply though.
WindowsDomain = "example.org"
Set WshShell = WScript.CreateObject("WScript.Shell")
Set WshNetwork = CreateObject("WScript.Network")
Set User = GetObject("WinNT://" & WindowsDomain & "/" & WshNetwork.UserName & ",user")
SplitName = Split(User.Fullname, " ", 3)
Dim Initials, NamePart
Initials = ""
For Each NamePart in SplitName
Initials = Initials & Left(NamePart,1)
Initials = Left(Initials,3)
WshShell.RegWrite "HKEY_CURRENT_USER\Software\Microsoft\Office\Common\UserInfo\UserInitials", Initials, "REG_SZ"
WshShell.RegWrite "HKEY_CURRENT_USER\Software\Microsoft\Office\Common\UserInfo\UserName", User.Fullname, "REG_SZ"