ACSC says that 226d and 227d have an impression displaced upwards by "almost 1mm." Here is the ACSC illustration with a detail blow-up:
Now given that the perf holes are about .75mm, the blow-up image would indicate that the displacement could be less than half the diameter of the perf hole, or as little as 0.35mm.
I have a number or strips of 2 or 3 stamps where the displacement is visible by eye. Here is an example where the displacement falls into this range:
So is this actually ACSC 226d (it is watermarked paper) or is it just a case of acceptable production variance. And does anyone know what that would be? I ask this question because some of the variances I have a quite a bit less than 0.3mm. I have a strip similar in appearance to the ACSC example, and even have one where one is actually lower than the other two so, by definition, this can't be 226d, as per the following images:
Your comments and hopefully explanations will be much appreciated.