 For example, forgers have fabricated many supposedly valuable postal covers by adding genuine stamps and forged postal markings to pre-stamp covers.A cover can be shown to be genuine if a genuine cancellation "ties" the stamp or stamps to the cover; that is, if a genuine cancellation runs continuously over the stamp and adjacent portion of the envelope, although one still may need to rule out the possibility that the cancellation was added later.Similarly, stamps that were cut in parts and used for a portion of the full value as splits can only be shown to have been so used if a genuine cancel ties the stamp to the cover or piece of cover.