Is the size of his brood nest smaller than yours? Maybe Greg's bees have created a honey barrier that is blocking the queen from enlarging the brood nest and your bees haven't? Just a couple of possibilities to consider that I've gleaned from others with more experience.
I have also been reading Walt Wright's articles about swarming in the "Point of View" section of BeeSource. He has some provocative thoughts about how and why a colony swarms.
His articles can be a bit hard to digest, but I really think he makes some good points that apply just as well to TBHs as well as to Langs. One article appropriate to this topic is this: "Swarm Preparation" Another germane article: "Is It Congestion?".
Walt identifies two types of swarms -- reproductive swarming and overcrowding swarming. According to Walt, the triggers for each type are somewhat different. From "Swarm Preparations":
"...Species survival by generation of the reproductive swarm is the basic objective of every over-wintered colony. The whole build-up period is dedicated to increasing the population to support division by the reproductive swarm. Division needs to occur in time for the offspring swarm to have a chance at getting itself established that season...."
"...Overcrowding swarms are the result of another survival trait of honey bees. To protect survival of the existing colony (priority one) a swarm is generated to reduce an out-of-balance condition of excess population. That swarm is generated later in the growing season than the reproductive swarm and is expandable...."
I wonder if Adam's swarms were from overcrowding -- where the brood nest had gotten so large and there are so many bees, that the hive simply could not support them all.