When Snow Leopard was released in 2009, both its installation DVD included with all sold Mac machines and the retail DVD that could be purchased directly through Apple included version 3 of the Boot Camp Windows drivers. Throughout the version 3.x lifecycle, several updates were released - 3.1, 3.2 and 3.3 can still be downloaded from the Apple website and each makes it explicitly clear that it requires the previous version to install - see the following URL for an example (See the "System Requirements" section):
So - my question. If you are trying to install Windows 7 on an older Mac model (let's take the MacBook Pro Early 2009 as an example), the latest version of the Boot Camp drivers to support this particular model would appear to be 4.0.4033 (https://support.apple.com/kb/DL1630) - however, what isn't clear from this download page is whether a previous version of the drivers need to be installed - as was the case with Boot Camp version 3.x.
Would anybody be able to clarify: can Boot Camp 4 simply be installed onto a freshly-installed Windows 7, or must an older version of the drivers be installed beforehand?