In this case a team could work across the project. One on the parser/lexer one on AST translation, one of code generation, Two on the runtime and 1 on build/ci. I think that makes 6.
You either never read the book or are interpreting it wrong.
The premise is that as you add more people to an EXISTING project, the amount of time it will take to complete will increase. However, if all of those people are involved from the beginning, then you are not subject to the same phenomenon - within reason of course.
So while it might not be "6" developers working on it for a year, it could potentially be 9 very devoted developers cranking this out with good results towards the end of the year.
Brookes also talks about another issue, that in a team of 6 there are (6 choose 2) edges in the communication graph. I think this is what kyriakos was referring to.
Errmm, if you actually read the book properly you'll realise that the baby/mothers analogy applies to synchronous sets of work and workloads that cannot be broken down into parallel running tasks. Once architected to a suitable degree I'd imagine that there are at least a few streams of work that could be carried out concurrently.
AFAIK they have about 20 people on this....unless I've mis-construed a friend of mine's elliptical comments. In other news - when is Google's VM that all the people they hired from the CLR team going to be released?