The Buffalo Bills have been an enigma in 2017.

According to ESPN's Football Power Index, the Bills enter Week 15 as the fourth-worst team in the NFL -- worse than the San Francisco 49ers (3-10) or New York Giants (2-11). ESPN's FPI gives the Bills a 12 percent chance of making the postseason. Buffalo ranks 26th in yards gained per game this season and 23rd in yards allowed.

Yet as the regular season heads into its final three weeks, the Bills have a winning record, 7-6. They are tied for sixth place in the AFC with the Baltimore Ravens and Los Angeles Chargers. Two of Buffalo's remaining games are against the Miami Dolphins, currently 6-7.

The Bills played their best football in September and October, but they have endured a brutal stretch of four losses in five games to emerge with one of the best chances at the playoffs in recent franchise history.

Buffalo's 7-6 record is tied with four other seasons -- 2014, 2007, 2004 and 2000 -- as the best mark through 13 games since the Bills made last the playoffs in 1999.

What went wrong each of those seasons? Here is a refresher:

2014: The Bills' strongest defense of the past decade stifled the Green Bay Packers, then 10-3, in Week 15 to improve to 8-6. Aaron Rodgers' 34.3 passer rating in that game remains the worst of his career. The Bills then traveled cross-country and allowed the Oakland Raiders, then 2-12, to extinguish their playoffs hopes. Buffalo rushed for only 13 yards, while a 51-yard catch by then-Raiders and current Bills wide receiver Andre Holmes in the fourth quarter was the marquee moment of an Oakland upset win. The Bills defeated the disinterested New England Patriots in the finale to finish 9-7 before coach Doug Marrone quit three days later.

2007: The Bills lost 8-0 to the Cleveland Browns in a Week 15 lake-effect snow storm that defensive tackle Kyle Williams compared to Sunday's win over the Indianapolis Colts. Losing to the Browns knocked the Bills out of playoff contention. The next week, Bills quarterback Trent Edwards completed 9-of-26 passes for 161 yards, with two touchdowns and three interceptions, in a loss to the Giants. He followed that by completing 16-of-30 passes for 133 yards in a season-ending loss to the Eagles.

2004: This is still considered the Bills' closest shot at making the playoffs since 1999. After the Bills won four consecutive games to improve to 7-6, then-quarterback Drew Bledsoe led Buffalo to two more wins over the Bengals and 49ers to enter Week 17 with a 9-6 record. The Steelers, then 14-1, rested running back Jerome Bettis and then-rookie quarterback Ben Roethlisberger but still managed to win the finale with Tommy Maddox under center. Buffalo got a required loss by the New York Jets but blew its chance at the playoffs.

2000: This season began the Bills' current 17-year playoff drought. Then-quarterback Rob Johnson threw two interceptions in a Week 15 loss to the Colts, dropping the Bills to 7-7 and eliminating them from playoff contention. Johnson was injured in Week 16 and replaced by Doug Flutie, who went 1-1 to finish the season 8-8.