G'day Chuck.

I don't think you missed the forest at all. Most of us who have built a Pfalz DIII/a have just accepted the inaccuracy as correct.
When WNW released their DIIIa the question was asked, hey, did they get it wrong? There appears to be a few wing panels missing.
The following is a reply to Stephen Lawson of Aeroscale, by Richard Alexander, posted on the Aerodrome forum in Jan 2011.
I think you will find it of interest.
Stephen posted: In doing my kit review I had several discussions with Mr. Richard Alexander of WNW and I mentioned to him the issue here and though I am addressing it in my review he sent along this bit of information. I'll post it here before things go too far off base.
"Hi Stephen,
Interesting thread and I suppose not entirely unexpected. I'm sure you
probably know much of this anyway, but just to clarify our position on the
'missing wing panels' and answer a few of the questions being asked. . .
The wing fuel tank was on the inside of the Pfalz D.III and D.IIIa upper
wing. It was covered with the ply that skinned the center section and was
not visible on the upper surface of the wing (other than the faired in
filler tube/cap protruding through the wing).
I don't know exactly when the myth of it being a detail visible on the
outside of the wing began, but it appears to have been started by an early
draftsman misinterpreting the Pfalz D.III drawings in the Flight capture
report. In the original Flight report the internal wing tank was drawn
with dotted lines to indicate that it was an internal detail.
Additionally the wing tank is not visible in any photo of a Pfalz D.III or
D.IIIa that I have ever seen (other than certain crash photos where it has
fallen out of course).
The lower wing root panel which is 'missing' is a reinforced walk strip
presumably intended for a mechanic to stand on while he makes final engine
etc adjustments before flight. These don't appear to be on every airframe
and when they are, they're not a standard size. It was not possible to
confirm if these were on any of our colour schemes, let alone what shape
they would be if they were. A pretty simple thing to add if you feel your
model needs it (check the reference photos in our instructions and on the
website for the shapes and sizes).
The 2 smaller hatches on the upper surface of both lower wings are covers
for the point where the aileron control cables are connected to the cables
coming from the control column. These hatches are hinged at the front and
held down by 2 turn buttons at the rear.
The wing attachment lugs are covered by the 4 smaller hatches under the
lower wing. These were also hinged at the front and held down (up?) by a
single turn button.
I hope this clears things up a little.
Regards
Richard"
Stephen added that the first time this myth was moulded into plastic was with the Aurora 1:48 kit!

I would like to repeat that your Pfalz is excellent indeed and I very much look forward to viewing your next.