I think you and gp may be speaking about different stages. Gp seems to be saying that a plane being designed and specified today would use technologies hardened against this type of error.

That even though they’re in widespread operation today, the aircraft types in question were designed (and certified) many years ago, before ECC was the norm. My impression is that, once their type is certified, new airframes are built to pretty much exactly that specification even all these years later.