We'll admit that we've used the phrase "Core Four" on this site, as over the past couple of seasons, it served the purpose of distinguishing the four players — Derek Jeter, Mariano Rivera, Jorge Posada, and Andy Pettitte — who'd come up with the club in the nineties and were around for the transition to the new stadium and for the 2009 World Series championship. But now that Pettitte has hung up his spikes, it's time to retire the term too, because it's always been kind of misleading.
Descriptions of the foursome usually mention that they all made their major-league debut in 1995, or that each has five World Series rings with the Yankees. And both of these things are true. But while Jeter, Rivera, and Pettitte were all important parts of the 1996 World Series team, Jorge Posada was not. He played just eight games that year, half of which came after the team had already clinched the division. He did not play in that postseason, and he made his first real contribution to a World Series winner two years later, in 1998. (Even Posada's own foundation tends to overlook all of this. It created a brand of sangria called Cinco Anillos — translation: Five Rings — and explains on its website that its name "symbolizes the five World Series rings earned and achieved by Jorge Posada as an All-Star catcher and one of 'the core four players' for the New York Yankees.")
Meanwhile, another homegrown player, Bernie Williams, hit his prime just as the Yankees began dominating the major leagues in the late nineties. A key contributor to four World Series teams, Williams made the mistake, it seems, of debuting four years before Jeter, Rivera, Posada, and Pettitte — and playing his last game four years before the next of that batch would announce his retirement. (On a related note, Bernie may officially announce his retirement soon. One would think it's about time.) And it could be another four years before the last of these players calls it a career: Jeter, as you may have heard, recently signed a new contract, with a player option for a fourth year.
All of which isn't to knock Posada or sing the praises of Williams (or to point out that — if the phrase "Core Four" is meant to note the final four remaining members of those dynasty teams — Pettitte played three years for Houston in between stints with the Yankees). But, even if the discussion is limited to homegrown players who came up through the fertile Yankees farm system of the nineties, Jeter, Rivera, Pettitte, and Posada alone did not make up the "core" of anything. They just lasted a bit longer than Williams, just as Jeter will presumably last a bit longer than the rest of them. The emergence of key contributors was a bit more staggered than the phrase "Core Four" lets on. And that's every bit as impressive, even if it never led to a catchy nickname.