well it's an accumulation of both actually. The calyxes (pods with hairs) do grow on top, beside, underneath etc of one another accumulating a "bud". Later in life the calyxes swell around harvest time. They also swell when pollinated, but that is not what we are talking about here. As far as the smaller "popcorn" buds lower on the plant where there is a lot of stem space between nodes and bud sites, how big they get depends on a lot of different things. Strain, conditions etc.. The question of whether or not they will grow up and connect with the larger buds depends on internodal length. If there is a lot of space between nodes and buds then you can well assume not. Some of those popcorn buds can grow to pretty good sized all in themselves. It also depends on strain, how much light they are receiving, and general grow room conditions. Most of your yield will come from your top main cola buds and the bigger buds right underneath those. Depending on your plant size and quantity, those little popcorn buds can add up in weight though.
Hope this helps.
Good luck,
Elway