Well, I was a bit late to this party. From the thread title I did not know a parcel post stamp was involved.
I agree the the accurate comments above, reperfed, individual perf wheels, to improve centering, best from the back and wild guesses not in interest of knowledge.
There are two points I wish to bring up. First not all reperfing is done to improve centering. This Q-10, 50 PP stamp was printed (as were all 17 PP and PP Due values) in sheets of 180 images which was then cut done the center lines to make 4-45 image panes. This results in 8 of the stamps with one edge straight and 1 with two edges straight (forming a corner). Thus in normal production and release 20% of all issued stamps have a straight edge.
Then remember from above, "cut down the center lines" means that a line of the same color of the stamp was used as a guide for when to cut. Some straight edges got the entire line, part of the line and none of the line. This means the real perforated stamps, if centered better than deep average, should have no stamp color on the perf tips. Some examples of reperfing on these (and similar straight edge panes cut along the guidelines) the faker leave a bit or a lot of such center line still visible on the perf tips.
Lines, top with part, right with full, corner with part and full as well as Shanghai cancel: