zoomx:
This way the last segment has not the same length of the others, for sure is longer, and you don't know how is long because you can get the same value, 1023, also for 5.5V, maybe more, maybe less.
In other words 1023 mean a value that is bigger than Vref-Vref/1024 (not Vref!) but you don't know how many is bigger.
Yes... this does not mean the estimated voltage you get by dividing by 1023 or 1024 is not a possible value, right?
you could even argue that given it's not at the beginning of the interval, if your setup allows going beyond 5V (not recommended though) then you'll be closer to the truth by saying 5 versus (5 - 5/1024) and statistically in the case lower the max potential error.
but as said above as well it does not matter compared to all the other imperfections of the hardware and likely your Vref