UL means upper left pane position. For this particular issue, the press sheet of 200 stamps were produced as 4 panes of 50 stamps each. The cut panes (often called mint sheets) are what we buy at the post office. The panes are IDed by plate number and pane position (UL, UR, LL, LR).
Your plate block is from the correct plate number, but from the incorrect position of UR.
The 19 means the 19th stamp in the pane (not the plate block), where the stamps in the pane are numbered starting with the upper left corner, then going across each row. So the 19th stamp is the 4th stamp in the 4th row (the pane is 10 rows by 5 columns of stamps).
So even if you had the correct UL plate block, you still would not see the plate flaw.
Also, for clarification, one of the red stripes is NOT missing. Rather, the red stripes are shifted so that one red stripe is masked by the capsule gridwork.
One of my favorite space stamps. Thanks for posting the pic!

k