The 2CV never had a second generation, which is why this entry spans the whole of 1948 to 1990. The engine grew from 375 cc to 602 cc and the power roughly tripled, but the car underneath was the one Citroën showed in 1948, and Wikipedia treats it in a single article rather than a set of generation ones.[1] The evolution lives in the trims below instead.
Two of those trims are worth pausing on. The 1981 Charleston is less powerful than the 1970 car (29 PS against 33 PS) and faster, because a milder camshaft and a different carburettor traded peak power for a longer-legged top speed. And the Sahara had two engines, one per axle, each with its own gearbox and fuel tank, worked by a single lever. Its power cell is empty: each engine is published at 12 PS, but adding two engine ratings together would be arithmetic, not a measurement.
The drag coefficient of 0.51 sits on the earliest trim because that is the year the source gives it.[2]