Last fall, the Patent Trial and Appeal Board (PTAB or Board) interpreted the IPR joinder provision, 35 U.S.C. § 315(c), to require joinder requests by a non-party to an ongoing proceeding.  (Target Corp. v. Destination Maternity Corp., IPR2014-00508 and IPR2014-00509.)  Prior to that decision,  the Board had interpreted § 315(c) to allow for issue joinder by the petitioner of the original proceeding (see, for…