There is no doubt that all impressions produced from a steel roller on a steel plate must be identical in every respect unless the plate is worn or inking vagaries apply. Every printed plate number MUST be identical in its shape and position to the next.
There is also absolutely no excuse for a pristine plate, such as Plate 77, a plate that only printed a handful of sheets, to print plate numbers that are anything other than clear and identical every time.
There are no “acceptable tolerances” in this case as far as the shape and position of the number ‘7’ is concerned.
This page illustrates that major differences between the 7s from the accepted Plate 77 stamps do exist. These differences can not exist if the impressions were produced from one, the Plate 77, roller.
Illustrated below is an image of a block of Plate 90 stamps from this issue that clearly demonstrates the fact that the plate numbers are identical.
Illustrated below are enlarged images of the ‘7’ on the right side and left side panels on the accepted ‘Plate 77’ stamps.
The fact that there are visible differences between the 7s must cast doubt in the mind of every serious philatelist who has an interest as to the way that these iconic stamps were produced
Illustrated below are images of the other two accepted Plate 77 stamps PI and LL.
It is unfortunate that sharp impressions of these stamps are not to hand. However, for the sake of completion, a focus on the 7s is illustrated which again indicates that these two stamps, as with the others illustrated above, again do show anomalies in the shape and position of the 7s.