I wish this was a bit more specific -- how long exactly is "several weeks"? 3 weeks (total growth of 33%)? 7 weeks (total growth of 95%)? 13 weeks (total growth of x3.45)? 52 weeks (total growth of x142)?
I wonder if a good way to explain this would be via examples of (starting point, growth rate, duration) tuples and an "interesting" / "not interesting" assessment for each. (Can YC publish anonymized data on its portfolio companies?) This would allow readers to look for an example which roughly matches their performance -- which may sound silly to people in the valley who are surrounded by startups all day long, but there are a lot of us outside of the valley who rarely meet anyone working for a startup and never see any sort of concrete numbers like these.
I absolutely agree about keeping the guide short though -- this is more a matter of something I'd like to see you (or someone else at YC) write more about in the future.