Long time ago I bought from a dealer a selection of stamp types that he had catalogued. He broke the issue down into 7 types summarized below.
Type 1 - Fluorescent paper with variegated blue printing and 10-15% "paleface indian" with a blue color shift down producing uneven margins around text in light blue area and above/below globe symbol.
The Variegated blue printing causes different patterns of light and dark blue ares mainly seen on wings and on shading of people around globe.

Type 2 - Just like type 1 but with minimal blue color shift and therefore even margins.

Type 3 - Plain paper with variegated blue printing and 10-15% "paleface indian" with a blue minimal color shift.

Type 4 - Plain paper with uniform blue printing and no "paleface indians"

Type 5 - Plain paper with variegated blue printing and all stamps show "paleface indian" variety

Type 6 - Med. Fluorescent paper showing Dark Blue wings and no "paleface indian" variety

Type 7 - Plain paper with variegated blue printing with "world misprinted" (splotches in globe) and all stamps show "paleface indian" variety.

I do not have enough of these stamps to prove these 7 types but I am assuming that the dealer that I bought this from did.
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