The only 1918 type 2 Christmas Seal issued in sheet of 100 was imperforate; All other 1918 type 2's were from booklet panes of 10. Except for a few, nearly every seal from the 15 different type 2 booklet panes of ten are straight edge. The 7 1918 panes listed below yield a few type 2 seals perforated on all four sides (P4S), or non straight edge seals. These 7 panes are scarce so, when intact, they should never be broken.
P4S Perforation 12 1/2
1) Green's #18-2x5 (Scott #WX22m)1918 ty 2, perf 12 1/2, pane of 10, 2x5, straight edge on three sides (SE3S), perforated margin (PM) at left. This would yield 3 P4S seals. (Illustrated)
2) Green's #18-2x7 (Scott #WX22L) 1918 ty 2, perf 12 1/2, pane of 10, 2x5, SE3S, PM at right . (WX22L). This would yield 3 P4S seals. (Illustrated)
P4S Combo perf 12 1/2 & 12
3) Green's #18-2.9x8 (Scott #WX22k) 1918 ty 2 perf 12 1/2 with 2nd and 4th vertical rows perf 12, pane of 10, 5x2, SE2S, PM at top and right. This pane will yield 3 P4S seals, 2 are combinations per 12 1/2 & 12 (perf 12 1/2 x 12 1/2 x 12 1/2 x 12, and the other perf 12 1/2 x 12 x 12 1/2 x 12 1/2).
There is no 1918 type 2 perf 12 1/2 x 12 P4S seal.
Any 1918 type 2 non straight edge seal tied on cover is rare.
Also, there are 1918 type 2 panes with a varying margin (VM) at right and left, which will yield what might appear to be a non straight edge seal. These varying margins were created when some 1918 type 2 press sheets, with perforated or roulette vertical gutters were cut. A VM pane can show perfs, or roulettes on one or both sides, depending on how well the pane was cut. Sometimes, one side is straight edge, and the other side may have a tiny margin. Upon closer inspection, even though the perfs or roulettes are present, they are knife cut, not torn apart but cut apart.
4) 1918-2x4 (Scott #WX22f), pane of 10 (2x5) perf 12 1/2, PM at top, VM R&L (Illustrated)
5) 1918-2.2x4 (Scott #WX22e), pane of 10 (2x5) perf 12 1/2 x roul 9 /2, PM at tom, VM R&L (Illustrated)
6) 1918-2.4x4 (Scott #WX22h), pane of 10 (2x5) roul 9 1/2 x perf 12 1/2, PM at top, VM R&L (Illustrated)
7) 1918-2.6x4 (Scott #WX22i), pane of 10 (2x5) roul 9 1/2 horizontally, roul 12 1/2 at left, and perf 12 1/2 thru the center (vertically) and on the right side, PM at top, VM R&L (Illustrated)