Now for the Pane; The pane is as fresh and presentable as the day it was released by Canada Post. The Fieldstock Margin 'Staple Holes' are to be found at R10/3-R10/4 and fortunately no tears sometimes associated with the removalble of the Staple holding the Package as received by the Postal Outlet.
The Plastic Flow,It is to be found and viewed as a slight "doubling" of the design and can be and has been mistaken as re-entry, a retouch or just excessive ink flow or perhaps a worn plate. Collectors will recall this is to be found on both the 6¢ Black and here with the 15¢ Issue. It was due to the use of the intaglio plates post January 1968. The Plastic Flow stamps -- For the most part they are to be found primarily on the Right side of the pane and less so as you move from Right to Left along each row of stamps. I do recall a British 67' Collector years ago who provided some excellent examples of the Plastic Flow from the Left Side of the Pane. The Variety in this Pane of 50 has the better examples on the Right however, there is still evidence of it on other stamps just less so. The Doubling as you will find with some other Varieties appears to varying degrees. However, being visible makes it the variety though it is obvious that the better, the more predominat the variety, the greater the Premium --- eg Bk#58 with Security Numbers on the Tab of the Pane.
However, the Pane also contains some of those Centennial Printing varieties that you are probably only going to find in Harris. Sometime during the printing the Doubling seemed to affect other parts of the design. Look for Letters in CANADA, where you would sometimes see what looks like a dragging of the purple color on the left side of the Letters. It is not everywhere and naked eye visible on all stamps, just some more visbile than others where it appears more faintly. Here in the Pane I see it at position R3/3 and on the D in Canada.