Positions 91 and 92
Straight Edges at Left and Bottom Sides

Horizontal Spacing Between "O" and "B": 2.0 mm versus 3.0 mm 

Distance Between 2 Points
Left Stamp at 6.5 mm and Right Stamp at 7.5 mm

Extremely Scarce in Mint State
1938 JUNE 11: MANILA CIRCULATING
National Research Council official mail, 4c Double Rated Domestic Mail franked with Positions 91 and 92 pair (enlarged below).

Positions 91 and 92 Extremely Rare on Cover