Here is an update as to whether a double perfin is fake or not...BNAPS and the Greene Foundation with the help of gportch and Jim and Gary I have analysed my #0269 (Scott 269) stamp.
As you can see, I choose this one which has not just double perfin, but quadruple perfin on the stamp below.
I took two strikes of the "H" in O.H.M.S. perfin...Look at the similarities of the shape of the holes...This indicates the use of the same perfin punch and not a post made up punch.
Now, look at the picture below of a close up of the two punches...the rough feathery edges are at the back of the perfin holes indicating thy were punched from the front of the stamp.
This is a little rarer, in that it is a quadruple perfin strike...Any questions or comments.