Does that mean that you can build a 'division' with only 1 or 2 brigades...
I would imagine so, yes. Johan has said that we can custom build divisions in order to replicate the number of brigades that specific armies used during the War. Thus, I would imagine a two (or even one) brigade division would be possible.
Either way, I doubt it's hardcoded. It'll be a little line in a text file somewhere.