The back side of the iron must of course also be well level if a sharp cutting edge is to be ground. For this there are 2 possibilities:
They smooth the back side well (at least near the cutting edge)(see, for example, The flat bevel). It has these consequences:
more work during the first smoothing
You do not have to worry about the back side for a long time
the cutting edge is in the plane of the back side (good for chisels).
You use a rear micro bevel. Consequences:
less work during the first Sharpening
You need to renew them more often, but with little effort
bad at least for chisels, because the cutting edge is somewhat removed from the plane of the back side. This is not a problem for a plane iron.