Million dollar question. Yes OS is Official Stamp and depending who you Ask, some will say Perfins detract from the value, and some will say that a legitimate OS Punctures will increase the value.BTW, I do believe that it's also a reversed Perfin.
Perfins are a specialty all on there own nowadays.
The OS perfins of Australia and States will be found reversed, up-side-down and in some cases even doubled. It all depended on the way any particular sheet of stamps was fed in to the perforating machines.
The Canadian OHMS perfins can be found in 8 different positions and that does not take in to account the double or triple images.