Austrian Stamp Differens Size

One of the stamp has a picture that is 30,1 mm high, the other stamp is 31.1 mm high. Anyone who know why there are differences in size and if it has any value. Thanks

My guess is the differences are related to different levels of moisture in the paper when printed and different directions the paper might be placed in the press. As the paper dried after printing it would shrink slightly across the grain and not shrink with the grain. This is a pretty normal process found in many issues done with "wet" paper. The degree of moisture would affect the degree of shrinkage. My thought is the catalogs don't deal with it because it isn't traced to a certain print run with narrow/tall stamps and a different run with wide/short. They were likely pretty much evenly interspersed. Maybe they dampened a stack of paper, then printed with the stack gradually drying over the print run...