Duncan now has 13,770 rebounds in his career, one more than Unseld (13,769) and 22 more than Hakeem Olajuwon (13,748), the latter of whom the Spurs power forward passed in last Friday's game against the Charlotte Bobcats.
Unseld accumulated his rebounds in just 13 seasons, averaging 14 boards per game in a career spent entirely with the Baltimore/Capital/Washington Bullets. (Yes, they were called the Capital Bullets for one year.) Generally regarded as the top player in franchise history, the 6'7" Bullets center played from 1968-69 to 1980-81 when there were more rebounds for the taking than there are in today's game.
That's not to say that Unseld's lofty rebounding numbers were merely a product of his era, as there's obviously something to be said for finishing in the top 10 in rebounding average nine times over the course of a 13-year career. For a point of comparison, Duncan has finished top 10 in 12 of his 15 completed seasons, and he currently ranks tied for 10th in the league with 10 rebounds per game in 2013-14.
While Unseld's one-championship resume obviously doesn't stack up to Duncan's incredible body of work, comparing the two big men serves to highlight an interesting aspect of NBA history.
The league's all-time rebounding list is dominated by players from the 50s, 60s and 70s when it wasn't particularly unusual for a player to average 15 or more boards per game. Those players benefit in the record books from higher per-game averages, while today's players benefit from improved medical technology and coaches who are (sometimes) more cognizant of their stars' long-term health.
Duncan is perhaps the best example on the modern side, as he's still an elite power forward at the age of 37 and likely has at least another year or two left as a high-impact player. Despite never topping 12.9 boards per game in a season, he has an excellent shot to finish his career as one of the six most prolific rebounders in NBA history.
The likes of Wilt Chamberlain (23,924 career boards) and Bill Russell (21,620) are well out of reach, but Duncan should easily pass Walt Bellamy (14,241) and Nate Thurmond (14,464) on the all-time rebounding list next season, and the Spurs forward also has a chance to pass Robert Parish (14,715), with an outside shot at Karl Malone (14,968).
If he doesn't catch Malone and Parish in 2014-15, Duncan would presumably have an excellent chance in 2015-16, assuming he's still playing.
Furthermore, given their respective career trajectories, Duncan figures to slide ahead of Brooklyn Nets center Kevin Garnett (14,170) at some point within the next year or two. When all is said and done, Duncan will likely rank sixth on the all-time rebounding list. He's still 2,442 boards away from fifth-place Moses Malone (16,212), and while it isn't crazy to think that Duncan could catch Karl Malone, we have to draw the line somewhere.