The model name Centennial applies to S&W's revolver with the completely enclosed hammer that was introduced in 1952 to commemorate the 100th (Centennial) anniversary of the company. Originally called the Model 40 in steel and the Model 42 (Airweight), the two models were later discontinued. The drive for double action only handguns was one cause for the reintroduction of the enclosed hammer model. When reintroduced, it was in stainless and called the 640 (following S&W's model numbering which was to put a 6 in front of the number to signify stainless). If I recall correctly, the first reintroduction of the 640 intentionally had the CEN-prefix, and they were also laser engraved in the frame window "Tested for +P+" or something to that effect. At the time, that was a big deal. The 640 might have been the only S&W up to that time sold on the commercial market which was specifically approved for +P+.

In any event, the name Centennial applies to a J frame with the enclosed hammer (40, 42, 640, 442, 642, etc.), the name Bodyguard applies to the J frame with the shrouded hammer that you can still cock for single action firing (38, 49, 438, 638, 649, etc.) and the name Chief's Special applies to a J frame with a fully exposed hammer (36, 37, 60, 637, etc.). To make matters more confusing, S&W has from time to time offered the Chief's Special with a bobbed hammer in double action only (37, 60 and perhaps other model numbers for the Chief's Special).

Whether the Centennial is more valuable or not depends on what the purchaser wants.