You're not really looking at this correctly.
Being a professional composer means you compose to sustain yourself from the income. You're not a professional when you score a certain number of titles, you're a professional when your composing is sustaining you financially.
A video game composer is someone who's done music for a video game, whether it be a free, indie or AAA game.
You're looking at it as a number of titles, but it's not that at all.
It depends on how much each developer pays you for the project. For instance: I was taking to an OCR game composer once, and he hasn't done many titles, but a recent title he did sustained him financially for about half a year. If you continually do projects, you can keep going with that as your sole income. It's not a set wage for a lot of people.
It's a contract thing more than an "I hire you to do game music" thing. If I do a AAA game that lands me tons of money, I'm not going to need to be doing as many games as another guy who hasn't gotten that much for his projects.