the 2526 is a very collectible watch and prices have skyrocket, the last 5 years. As such, some collectors have treated the classic 2526 as a "commodity" and thus have been flipping them for a quick profit.
The 12-600at movement (arguably one of Patek's all-time finest movement) were produced from 1953 to approx. 1960, with a total of 7099 movements produced (not all cased) ,amongst 10 different models (including the 2552). It's safe to say not a lot of models, equipped the 12-600, were produced.