Let's be clear, does the policeman misremembering and event change what actually happened in anyway? If not then I guess, NO it isn't relevant.
Look, you are making a leap that is very normal for people to make, but still incorrect. What is being unsaid is that you are accusing either side of lying to cover up and thus the lying person must be a bad person worthy of punishment for that reason, or at least unreliable in some other way.
Someone mentioned that the defendant should be given access to evidence also before making a statement if the cops should. Funny thing is that isn't a gottcha against me, I agree completely. When you look at the most egregious cases of abuse and false imprisonment, the cops playing the same kind of tricks by deliberately withholding evidence are pretty much central to all of these cases.
Trying to trip up people looks great on Perry Mason, but in the real world it is subject to abuse. It is a very dangerous tool to use in our justice system, even if it has good results sometimes, it dangerously undermines peoples confidence in the systems when it goes tragically wrong.