Sometimes you can’t tell the players with a scorecard.

For an undisclosed reason – we’re guessing some kind of locker-room bet or competition – many of the defensive players wore another player’s jersey for practice. So, no, that No. 63 who was jogging around the field is not the Jets suddenly extra-undersized nose tackle, but Justin Miller wearing Dewayne Robertson’s jersey.

Also, Kerry Rhodes was in Victor Hobson’s No. 54, Darrelle Revis was in Jonathan Vilma’s No. 51, Shaun Ellis was in Andre Dyson’s No. 21 (man, did that jersey look like it shrunk), D-Rob was in Miller’s No. 22, Eric Smith wore Eric Barton’s No. 50 and Brad Kassell was in Drew Coleman’s No. 30. There were others but, frankly, you get the picture.

Also from practice, this blog and most of my fellow Jets’ bloggers have long since stopped reporting on the Jets’ musical selections – it was news for a week or so at the beginning of Eric Mangini’s first training camp – but today was kind of amusing.

Since the Jets are going to Philadelphia to play the Eagles Thursday night, practice had a Rocky theme. “Eye of the Tiger,’’ was followed by a Sly Stallone snippet of, “Hi, my name is Rocky Balboa,’’ which was followed by the iconic theme song.

I wondered aloud whether we’d get a “Yo, Adrianne,’’ which, for the Jets, could be “Yo, Adrien/Adrian,’’ Clarke or Jones.

Meanwhile, running back Thomas Jones repaired to the back field to do leg stretching exercises. Can’t wait to see him Week 1 vs. the Patriots.

Meanwhile, more good Xs and Os talk from Mangini today on how cornerbacks should play wide receivers. Honestly, not making fun of Coach at all, I really enjoy this stuff because it is informative. Mangini dissected how the vertical part of a receiver’s route once they release off the line of scrimmage and before they break into their cut is called the stem.

The discussion started when Mangini was asked for an example of what first-rounder Darrelle Revis is still catching up with after holding out for 20 days. Mangini used an example from practice.

“You want the DB to be able to close the relationship, the cushion between him and the receiver to be as tight as possible and it’s really key,’’ Mangini said. “Ty Law was one of the best I’ve ever seen at that, where if he made a mistake at the line of scrimmage, he made up for that mistake in the stem.

“Darrelle had so much separation in the stem. he had done a nice job at the line of scrimmage and the receiver was able to gain back the ground that Darrelle had won and run the route successfully. Even though the transition was difficult at the breaking point, if he had done a different job at the stem, he would have shut down the route.’’

Meanwhile, two Jets’ events tomorrow. The old Sack Exchange of Mark Gastineau, Joe Klecko, Marty Lyons and Abdul Salaam will ring the opening bell for the New York Stock Exchange tomorrow morning along with Jets owner Woody Johnson.

Also tomorrow, the Jets will hold their Kickoff Luncheon at Cipriani Downtown Restaurant in Manhattan. It helps raise funds for various charities, including a lupus charity.

And on Sept. 23, ex-Jet wide receiver Wayne Chrebet will be honored at halftime of the Jets game against the Dolphins.

Meanwhile,  Eric Mangini, trying to hold back a sly grin, wins the corny line of the day award after being asked why Curtis Martin still had a locker in Jets room.

“Because he’s Curtis,’’ Mangini said (wait, it gets better). “Curtis still has a presence in the building. And I love having Curtis around. He’ll always have a locker in the Jets’ fans’ hearts.’’

Finally, kudos and congratulations to Newsday’s Tom Rock, who became the latest member of the Mangini-said-his-name-at-the-press-conference club. Rock joins charter members Cimini, Cannizzaro, Crouse and Hutch, though, other than Hutch, everybody’s addressed by their first names. Me, Pelzman, and Waszak of the AP are still waiting for our buttons