Like many “best of” compilations, the Buddy Holly double-disc Down the Line: Rarities and the Holly triple-disc Memorial Collection (both Geffen/Decca) possess an air of unreality. Listen to a select body of an artist’s mature work—no album filler, no learning curve detectable in the songs—and you get the feeling that it all sprang spontaneously into existence. This sense is especially pronounced in the case of someone as prolific and gifted as Lubbock’s Holly, who released five classics in 1957 alone. In the two years he had left, Holly went on to record an array of tracks brimming with innovation, freshness, and exuberance. But these collections strive to humanize him: They capture the halting student as well as the effortless composer. Both sets begin in Holly’s country days, and you can almost pinpoint the moment when Elvis rolled into town. Rarities’ “garage tapes” include several covers, in which Holly tries on his rock and roll shoes. On numerous demos and outtakes, it’s fascinating to hear him find his footing. The hits and misses on these first-rate collections provide genuine insight into a monster talent.