The perforations are made by organisations, usually to deter theft of stamps by employees. In general, perfins will reduce value - except, of course, to a perfin collector. As these are all common stamps, my view would be that they add interest.
They are perfins. Usually made by a punching device and used by companies or government to mark company initials or government department on them for further identification. It is an area of stamp collecting specialization. Some can be valuable depending on scarcity.