Ultimately, this is trying to solve a human problem with tech, which is rarely a solution. If a display has garbage data on it because it's broken, the untrained person trying to read it is going to misread it regardless of the failure mode.

That and you can make 7-segment displays fault tolerant, ie, detecting when segments are out/partially out, because you can measure current draw. Not exactly difficult, also not exactly common because they don't really fail that often.