Vocalist/producer Lyn Stanley has established herself as a foremost stylist of the Great American Songbook. That is no mean feat. The sheer amount of vocal music made each year around the Songbook is impressive. It is too bad that the quality of a great many of those recordings is not equally impressive. Stanley’s two previous recordings, Lost in Romance (Self Produced, 2013) andPotions: From the ’50s (Self Produced, 2014), have been an evolving prelude to the present. “How Long has This Been Going On,” the opener for Interludes demonstrates Stanley’s command of the standard.