redwwodrandy thanks for the link. It's now clear that my stamp is a counterfeit. Cause of impression (not crisp like the original) and wrong perforation.
JLLebbert, John Becker you guys are right
Perforation on my stamp is 13.5
It was to be too good to be true. You guys had save me from an embarassing moment when the expert commitee would have a look at this stamp for certificatation.