I read it as both diets lasting 6 months, but one study did a follow-up at 1 year among those that lasted the first 6 months. That would explain the regained pounds in the 1-year study - if some of the 6-month dieters fell off the wagon in the 2nd 6 months.

We'll have to see the actual text of the studies to see what really happened, and that won't be freely available for another 6 months.