It seems that each link has a small to medium effect initially, but that effect increases over time. If you add a lot of links at once, you're not only going to see faster results, you're going to see much bigger results over time.
I think this is an interesting piece despite the small sample size. My experience and general theory is that Google doesn't assign full value to new links, in part because so many disappear within a month's time.
So perhaps a new link is work 10% in month one but then gains weight the longer it is alive until it's passing the full value.