NEEDSUPGRADE flag; how is it set?

[JeffTucker]

Our update installs are failing and seem to be running the install of the new version (later than what is on the disk) in Maintenance mode. The MAINTENANCE flag is true, and the NEEDSUPGRADE is false. What piece of logic is responsible for determining the status of the NEEDSUPGRADE flag? It does not appear in the msi code (I searched), only references with conditional logic.
I did check that the latest build of the setup is being run. It has the name "Build 7.0.343.0.exe" run out of the support directory.

[MichaelNesmith]

You probably forgot to generate a new revision code. This is always on auto-change unless specified otherwise.

NEEDSUPGRADE is discussed in detail in the help file pre-defined variables topic.

[JeffTucker]

Lets say I change a bunch of code in msi, save it, fail to manually change the revision code, commit it to our source control. In this scenario I do not build the project. Then the automatic build (on another machine) builds using miabuild.exe.

Does the revision code change after that build? Before building it? If before, then shouldn't the mpr file change? I see no evidence of that.

So is it the case that miabuild does not touch the revision number even when the setting is to update it automatically on build?