Apple has changed the way Combo updates work with the release of OS X 10.10.2. Previously an OS X Combo updater would patch all earlier releases of the OS version. Examples… The OS X 10.9.5 Combo updater will update 10.9.0, 10.9.1, 10.9.2, 10.9.3, 10.9.4, and even 10.9.5. In fact reapplying the latest Combo updater is a commonly used Mac troubleshooting step.

The OS X 10.10.2 Combo updater will only update OS X 10.10.0. You can’t run it on either 10.10.1 or 10.10.2. If Apple continues this trend when OS X 10.10.3 is released, it will change the way we support Yosemite.