Interim Fixes are not considered Maintenance Releases. They are released after the Maintenance Release (Fix Pack) in order to fix a critical issue which was discovered after the release of the Fix Pack, bu before a new Maintenance release is due out. They will usually be incorporated int he next Fix Pack when it is released. Additionally, when you issue the "Show Server" command from the server console, the Interim Fix will display as a Hot Fix, and not as a Fix Pack.