To add to what David stated. Upgrades include all the latest hotfixes as well BUT DO NOT include each individual major upgrade. For instance if you want to move from v9 to v11, you need to apply the upgrade from v9 -> v10, then v10 -> v11 individually.
One last point, it is never recommended to run on a vanilla version (9.0, 10.0, 11.0) of Kentico. When you start a project, immediately apply the latest hotfix.