Since the Irish accordionist Sharon Shannon signed with Nashville-based Compass, they have worked hard to get this wonderful musician attention in the U.S., where she has been underappreciated. Shannon has already put out a greatest hits collection, but this time she has issued a two-disc retrospective of her 15-year career. One disc features the instrumentals that made her one of Ireland’s most popular traditional musicians; the other is composed of songs with lyrics, which Shannon has only tried on her last two releases. Not surprisingly, the instrumental disc is excellent, with Shannon’s melodic button accordion eddying amid various effervescent ensembles. An exceptional instrumentalist, she has always been a generous collaborator, letting all the players shine as a whole and always serving the tune well. The second disc adds a few unreleased tunes, but some are also-rans. Highlights include Steve Earle’s “Galway Girl” and Sinead O’Connor’s achingly beautiful “Anachie Gordon.” Shannon ends on a duet with oldster Dessie O’Hallaran, whose worn pipes add character to “Say You Love Me” while the band builds steam behind them.