Knives P-9 (lower envelope), P-10 (middle envelope), P-11a (top envelope), and P-11b (second envelope from the top) compared. Knife
P-9 was used on the smaller size 5 envelopes. The rounded flap of knife P-10 was used on all of the size 6 envelopes produced in 1884
(the large size 10 envelopes used for some of the 10¢ value had knife P-12 - not shown), as well as the 1885 printing of the 1¢ value.
The pointed flap of knife P-11a was used in printings to fulfill printings of the 1¢ and 2¢ values ordered in January, 1889. The more
pointed flap of knife P-11b was used starting with the June, 1889 order and was used for all subsequent orders of 1¢ and 2¢ values.
Notice also the difference in the corner angles where the flap meets the body of the envelope. Knives P-11a and P-11b have wider
angles than P-10.
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