Different training methods that led to the weight gains. Chad was, for some reason i don’t know, power-lifting and his hypertrophy/muscle growth was additional fibers put on through lifting to failure… and that gain came over a short time frame, a matter of months.
When I went up in weight it was while using the methods we talk about in our book. I never did any hypertrophy training at all. And the weight gain was very gradual, probably over 5+ years, and after that peak of fitness I’ve never been so heavy again. I was 168 at peak fitness by every measure especially the subjective-feel. Right now I’m 155 and not even in the same realm of fit as I was in 04/05/06/07/08. Through all the time I was very low body-fat 6-7% when tested. To be totally honest I don’t understand exactly why I got heavier over that period but since my performance by every measure kept going up I didn’t worry about it.
So to answer your question, don’t think too much about your weight unless it’s an obvious problem in the sense that you need to loose some. But if you feel you’re generally close to your ideal weight, follow the training, let your body be shaped by it, and as long as your performance by both subjective and objective measures is increasing, then you’re golden. Hope that helps.