Too many country artists who start strong fall off artistically as they work their market niche. So Alan Jackson’s improvement is a triumph—his writing only peaked after he was sure his niche would listen. “Little Man” is populism without ressentiment, “Drive (for Daddy Gene)” makes me wish my dad had risked his Chevy on me, and “Where Were You (When the World Stopped Turning)” could end up one of the few 9/11 remembrances emotionally evenhanded enough for Americans of differing convictions to share. Then there’s the forgettable bonus disc, which demonstrates by contrast why some hits deserve to be. This clarity will dissipate instantly if you move on to 50 Number Ones. Few long-running pros have front-loaded their books like George Strait, whose no-frills approach started fresh and turned ticket to hackdom in under five years. The keepers presumably scattered across the second disc are hard to locate as you shake off the cobwebs induced by the first; conceivably the 51st track, the non-No. 1 “I Hate Everything,” only stands out because it’s placed first. On The Essential Merle Haggard, on the other hand, hackdom ages like a fine muscatel. Back when Hag was still flexing his muscles commercially and culturally, the sentimentality of his Billy Sherrill period was rank. Now it’s just gorgeously phrased. Sit back and enjoy it. No harm done.