Groups enduring 40 years and 31 albums together aren’t supposed to sound this invigorated. But as evidenced here, Baton Rouge’s Smithfield Fair does so by pushing its craft forward and not resting on its legacy laurels. “Love Is a Mystery,” the whirlwind opening track by Jan Smith, ranks among the group’s best songs with its peppy tempo, glistening background vocals and crystal-clear mandolin picking. The neatly dovetailed lyrics mention patience and sharing, time-tested attributes rarely mentioned in other amorous fare.

Love, of course, is the overarching theme. Many songs resemble a dialogue between husband-and-wife Dudley-Brian and Jan, who alternate vocals to offer various perspectives on their longstanding relationship. Dancing is also a reoccurring theme, as is spending quality time together in the solace of home. As lovestruck as the proceedings may seem, they are never gushy, uncomfortable or sickeningly sweet but sincere, honest and fireplace-cozy like a life together can yield.

Instrumentals offer a novel change of pace. While Jan has always contributed to Smithfield’s distinct folk-centric sound with her accordion, on two tracks she adds another dimension by playing piano. Her tinkly composition “The Bells of Evermore Cottage” is predicated on cascading high notes and swelling tempos; the gorgeous reading of J.S. Bach’s “My Heart Ever Faithful” finds her dueting with herself on accordion and piano.

Though everything makes its public debut here, some songs (“Love Goes Cold”) are decades old and were never released. Without this inside information, you wouldn’t know it since everything sounds amazingly warm and fresh as if it came out of the oven this morning.