I think our theories have some flaws in them, or the game has some code we aren't taking into consideration.
I had a Day Trader level 1 at $105/day marry a Boardgame Designer level 2 at $105 a day. They were doing well, getting the same pay, and I made them have a baby. Dad got a promotion while mom was carrying the kid. As soon as she put the kid down, she went back to her job Day Trading. Her next promotion, to level 2? Now her salary is only $90. Either a bug, or we don't know enough about the jobs to see everything. To me, it looked like she got demoted for not working for two years.
Actually, I think that's just a feature for that particular job. In the chart I made, I actually explained that would happen with that particular job. I haven't actually ever played anyone with that job, but another member, Lewanda, kept great records and that's what happened to her as well.
It's possible that there may be other jobs that are like that too though. There are so many available that I really don't know for sure yet.
**eta -- My original post is on page three of this thread.