National Parks Imperf 756-765 Question

I see ....
There are multiple plate numbers for each issues 740-9. ( Reference Durland Catalogue) The plate numbers of 740 correspond to 756 . The plates , ink and paper are the same . A re-perforated 756 could be compared to a 740 with an exact perforation measurement. Perhaps electronic perforation gauges will detect the re-perf. The thin film , aluminium gauges would fall short .

Do you have more info on 756 re-perf ?

The way to tell is by understanding how stamps were perforated at the time and looking for the pressure ridges that exist only on genuine perforations. Obviously if they gauge incorrectly it's a dead giveaway.
Knowing what perforations are supposed to look like for any given set or era is very important and requires real study, usually with a 10X and 15X glass on known genuine examples. With the Parks this is easy, since no one would reperforate any regular examples of 740-749.

Nice really nice. A great collection. I don't have even one of these Imperferets.

Good info !