An erupting wellspring of euphoria: that would describe the vintage swing emanating from Vince Giordano and the Nighthawks at the 92nd Street Y during Saturday evening’s season-opening program of Lyrics & Lyricists. It is challenging enough for a band to churn out museum-ready facsimiles of 80-year-old pop tunes outfitted with stylistically accurate period arrangements. But Mr. Giordano’s ensemble, like the Jazz at Lincoln Center Orchestra playing the blues, preserves old music with such deep affection and idiomatic understanding that the past becomes the present and the term “quaint” simply doesn’t apply. In its lighthearted way, the music swung as intensely as any being created today.