Not counting the 10 suits, a group like this only happens in Division I once every 1.8 years.

Now that Duke is rounding into form health-wise, this may be an appropriate moment to revisit the idea of the category 5 roster. With Mike Krzyzewski giving serious minutes to Jayson Tatum and the coach also saying that Harry Giles may play before Christmas, this epochal-roster-strength stuff is no longer a conceptual exercise where the Blue Devils are concerned. The speculative “when Duke gets healthy” dream pieces have been retired, and unalloyed present-tense adulation (heresy just two weeks ago) has begun in earnest.

A category 5 roster is one that returns at least 40 percent of its possession-minutes from the previous season, and adds a freshman class that rates out at 25 recruiting points or better based on Drew Cannon’s canonical front-loaded evaluative curve.

Duke has the nation’s only category 5 roster for 2016-17. Here’s how the Blue Devils and Kentucky fare on the metrics in question this season:

                           Recruiting
                %RPMs        points
Duke              56          36.6
Kentucky          26          35.4    

In other words the Wildcats match Duke step-for-step in terms of freshman talent, but fall short in the returning-experience department.

As a point of reference, here’s every category 5 roster “ever,” meaning in the one-and-done era.

                                    Recruiting
                 Year    %RPMs        points
Duke             2015      42          29.7
Kentucky         2015      60          26.8
Kentucky         2012      53          33.1
Kentucky         2010      70          30.1
North Carolina   2007      79          35.0  

(Yes, Wisconsin played one of the more robust two-game schedules to be found anywhere in the last decade at the 2015 Final Four — and very nearly went 2-0. Badgers, I salute you.)

Not all of these previous category 5 teams won a national title or even made it to the Final Four, of course. But they did all at least get to the Elite Eight and, perhaps most tellingly, they all earned No. 1 seeds. There are, thank goodness, no talent-secured guarantees after Selection Sunday, but the blend of experience and talent that Duke can claim this year has at least landed every previous such roster on the top seed line.

Why the importance of non-freshmen is heightened at one-and-done programs
I suppose this category-5 business fails miserably when subjected to the Bill James test of any analytic bauble, namely, that it be 80 percent reassuring but 20 percent surprising. It is instead 100 percent well-duh-level affirming to “learn” that a garden-variety Duke/Kentucky recruiting class matched with a healthy level of returning players will give you a solid shot at winning it all.

Certainly we would know that Duke is really good even if we didn’t bother to run its roster through these particular measurement hoops. I guess where this exercise has been useful to me, then, is on the “how” and the “why” of the matter, rather than “whether” or “who.” Basically, it may be the case that a teeming horde of insanely talented freshmen still requires the presence of a veteran or three in order to attain quote-unquote great-team status.

Freshman-heavy Kentucky will test that theory this season, and I for one don’t underrate the Wildcats’ chances of breaking free from history’s iron grip. John Calipari’s offense has looked outstanding, and if you want to question the Cats’ defense, well, throw a stick at the last 10 national champions (or the teams at the top of the current rankings?) and you’ll hit a solid number that were very good but by no means fearsome on that side of the ball. It needn’t be a deal-killer.

Nevertheless, until UK breaks this mold in 2017 we still don’t have an example of a painfully young team (one that returns less than 30 percent of its possession-minutes from the previous season) earning a No. 1 seed in the NCAA tournament. Kansas earned a spot on the No. 2 line in 2014 with a really young roster that featured Andrew Wiggins and, when he was healthy, Joel Embiid. (Bill Self is pretty good at what he does.) That’s been the ceiling so far.

To be sure, this is plainly a streak and not some innate ontological underpinning of the cosmos. (For starters, getting a No. 1 seed depends in large measure on the year in which you exist. Good luck in 2015.) Still, this “no top seeds for teams with more kids than can fit in a backseat” thing has shown itself to be a fairly hardy tendency.

The operational implication of this tendency for Coach K and Calipari would seem to be pretty straightforward. Carve out space in each recruiting class for guys like Luke Kennard and Tyler Ulis who will elude the next level’s grasp for two seasons or even longer. Categorically speaking these tend to be guys under 6-foot-8 or so (granting that Amile Jefferson is a jewel of an outlier) who can shoot. Such players are programmed to be relatively overlooked as freshmen but are invaluable over the relatively long haul.

Naturally you can win it all without going about this thing the Duke-Kentucky way. Not only did Villanova prove as much in a category-5-free world last year, an even better example is supplied by Duke itself. Back before Krzyzewski had his sincerest-form-of-flattery epiphany, the Blue Devils won a title in 2010 with players who were passed over entirely in the ensuing NBA draft. Moreover, to reach the championship game Duke had to first beat the team that did indeed defeat a category 5 roster.

So, no, don’t hand the Blue Devils the 2017 title just yet. In fact if only Jay Wright had a college-dominant Zoubek figure perfectly invisible to wearers of NBA goggles, I would really love the Wildcats’ chances for a repeat.