No question that the analogRead() returns ADC count values ranging from 0 to 1023, so 1024 possible values. Now if one should use 1023 or 1024 as the scaling value in any remapping of the value is a topic that always seems to keep coming up, with proponents for both values that claim it's a no brainer as to the correct value. I have no clue as to which is correct, but am surprised that it doesn't have a definitive mathematical provable answer.
Come on software gurus, put this topic to bed once and for all. ;)
Coming at it from a hardware guy I have a more practical 'answer', it doesn't really matter at all because as far as it effecting the accuracy of the remapping calculation as the 0.1% difference probably pails in comparison of the raw accuracy specification of the ADC and basing the calculation assumption that the Avcc reference voltage being exactly +5.000000 vdc, which is probably never the case.