A "50/50" usually references an edge. So on the cutting edge, it is an even 50/50 "V". It can be 50/50 at 12 degrees or 50/50 @20, but each sides angle is equivocal.
A double bevel is a knife design created by grinding. So from the spine to the cutting edge, there is a blade face that has been ground (most of the time)
. It can be a flat grind, a convex grind, a hollow grind, and any of these grinds can be symmetric (50/50) or asymmetric. So for instance, my Ginsanko Hiromoto Western Deba has an asymmetrical semi convex grind. It has a flat ground left blade face at around 30% of the total included angle and the right side blade face has a distinctly convex grind that is the other 70% of the total included angle, but the actual cutting edge has an asymmetry, as well. The actual cutting edge does not look like a "V" as it is, in fact, a 60/40 right-handed bias. It's a particularly unique blade, but exemplifies your point, quite well.