220.4A and 300.3B applied to neutral bar mounted in overhead wireway.
First of, let me start by saying I am not young. I may have been lead into some possibly non complying practices over the last 50 YEARS which is WHY i ASK QUESTIONS.
The SCENARIO IS A 480/277V PANELBOARD WITH 3 2" CONDUITS EXTENDING VERTiCALLY ABOUT 40" into a A 10 X 10 X 48" WIREWAY WHICH is attached up tight to the finish ceiling. Now, in the past, we always considered that assembly as one big panelboard and once the cable conductors entered that wireway, one could pretty much do what one wants with them...i,e, install a grounding bar in the wireway to run all the branch circuit grounding conductors and so the same thing with an isolated neutral bar which saves counts on the conductor fill of the 40" 2' pipe to minimize conductor derating.

I have been doing it this way for well over 20 years until today when I was inspected by the senior state of Maine electrical Inspector. He states that 220.4A and 300.3b prohibit doing that and all the individual neutral conductors associated with each branch circuit must go all the way to the grounded terminal in the main feeder panel.

Does anyone smart out there have an opinion on this?. At one time, the State of Maine electrician's examaining board had issued an adoption stating that they would consider all electrical equipment on the same backboard as the feeder panel part of that FEEDER PANEL AND ONE COULD INSTALL THE NEUTRAL BAR WHEREVER ONE WISHED AS IT WAS NOW IN THE PANELBOARD ASSEMBLY.[

The Inspector is right.
Be happy that you got away with a misinterpretation for over 20 years before you got caught.

I suppose 300.4(B)(4) could lead to this confusion but it does not appear that this condition applies. (2017)

The column width panels that I have seen over the years (few & far between) have had a neutral bar in the pull box section that was supplied with the panelboard as a complete unit. ie: 'Factory supplied' with documentation regarding the size of the neutral conductor stated.

As I said, few and far inbetween.

the adoption of 220.4 (b) IN THE 2011 nec CODE pretty much says I can't sdo that any longer but I still don't understand the concern especially with non-metallic conduits running between the panelboard and the metallic wireway 40" away.

A bit confused. The last time there was an Article 220.4 in the NEC was in the 2002 edition. In 2005 NEC articles in 220 were renumbered and 220.4 became 220.18. In any case, the old 220.4 and present 220.18 address maximum loads.