Jerry-
Thanks for your efforts. Did you recover those images on-line, or did you make a personal visit to the archives?
So, your new information adds to our understanding of plotting charts. My 1939 catalog does not offer HO5050 or any of its sheets: therefore, I conclude that HO5050 was withdrawn from public sale at some point between 1933 and 1939. As I have noted elsewhere, there is no special information on the plotting sheets, indeed, they contain less information than the nautical charts. I believe they were intended as a convenience item. Hence, there is no particular reason not to provide them to the public, and I doubt that Earhart or Noonan would have any particular difficulty in getting hold of copies if they wanted them.
HO5050 sheet #3, as you pictures show, cuts off at 2.5 degrees S, so it couldn't be used for the early part of the flight. As Ric notes, Sheet #3 does not show the Phoenix Islands.
It doesn't include Lae, New Britain, or Bougainville. So, IF Noonan used this chart, he would still need another chart for the first part of the flight.
Your index map shows that there are one or more HO 5050 sheets that cover New Guinea, but I can't quite parse it/them from the graphic. I think #19?
HO 5050 sheet 17 covers both North and South of Howland from the Line Islands to the Phoenix Islands. AE & FN would fly onto the map from the West near the Gilberts. It looks like a better choice to me for the last part of the flight than Sheet #3, because it allows for plotting positions both North and South of Howland. As in the case of #3, he would still need another chart for the first part of the flight.
Your images of a 1930s vintage HO 1262 identify the chart in the AE photo Ric posted pretty conclusively as HO 1262.
Lastly, I would note that Noonan's description of the charts he carried for the earlier Hawaii flight suggest that he was carrying a lot of charts that he was unlikely to actually need--particularly local nautical charts. This proves nothing about the Howland leg, but does suggest to me that Noonan's inclination would be to carry more charts rather than less.
adr