It has been the case in past history that Code revisions become mandatory six months after the date of issuance. If the ASME BPVC was issued on July 1, 2013, then it should be mandatory on January 1, 2014 as already mentioned by TGS4.
Is the 2013 edition available in IHS? I have not checked IHS lately.
Ever wonder why new Code revisions become mandatory six months after the date of issuance? The reason is to give ASME Certificate Holders (Manufacturers) the chance to update their Quality Assurance manuals. I recall this mentioned in a webcast (ASME or IHS website???) early in the year.