Quite a few conflicting theories here. Interesting. Here's the deal. Yes, they will absolutely grow bigger, and mature, and become much heavier and dense. The plant redirects its energy into maturing that part of the plant which still remains. In this case, the smaller buds on the lower branches. This happens all the time in nature, which is why you don't pick all the raspberries, or apples, when you see the top of the bush or tree is ripened. Sometimes people get too lazy or impatient, but patience (coupled with knowledge) pays off in harvesting. Give the bottom two more weeks. Yes, the growth is slow... because those buds have not hit stride yet, hence their immaturity in the first place. The only question is one of scalable resources, by which I mean, is it worth it to run your lights to mature your lower buds to peak. If your plant is small, the answer is likely no. If you've grow very large plants, and there's quite a bit of potential yield then the scale of resources necessary in relation to the potential harvest of mature buds would comparably dictate that you see the lower crop through to peak.