And here is the reference for what Bose said
http://fsims.faa.gov/wdocs/notices/n8000_364.htm
Added Ratings. If a person requests that a rating be added to his/her U.S. pilot certificate on the basis of meeting the appropriate pilot certification requirements of part 61 (i.e., the practical test and the knowledge test, if applicable), those requirements must be accomplished before the issuance of that additional rating. However, if the person requests the added rating on the basis of that rating having been added to his/her foreign pilot license, no knowledge test or practical test is required. The authenticity of the foreign license must be verified before adding the appropriate rating.