RTFM
Steht ganz klar in der Hilfe:
Initialize:
this method can be used on a computer with a Notes client or Domino server and bases the session on the current user ID. If a password is specified, it must match the user ID password. If a password is not specified, the user is prompted for a password as required and as the software permits. If the software does not support prompting (for example, VBScript under ASP/IIS), you must supply the password or the user ID must not have one.
InitializeUsingNotesUserName:
this method can be used only on a computer with a Domino server. If a name is specified, the InitializeUsingNotesUserName method looks it up in the local Domino Directory and permits access to the local server depending on the "Server Access" and "COM Restrictions" settings. The password must match the Internet password associated with the name. If no name is specified, access is granted if the server permits Anonymous access.
Bei Variante a), die Du nehmen MUSST, wird nicht eine gecachete ID verwendet, sondern die ID verwendet, welche in der NOTES.INI angegeben ist (die zuletzt im Notes-Client verwendete).