Other mistake: In the scene where Ryan joins Kelsi for early-morning rehearsal, Ryan sits at the piano and starts playing "Just Wanna Be With You." However, the sheet music only shows the melody, not the actual music, and this is the first time Ryan has seen the song, so he has no possible way of knowing how to play it.
Visible crew/equipment: When they are singing "A Night To Remember", with Ryan in the prop house with Sharpay in the bathroom (with the blue and pink background), there is a crew member reflected in the background colour.
Continuity mistake: During "Now or Never", Troy passes the ball to Chad who is standing on the left side (looking to the cheerleaders) of the white line drawn on the floor, but when he catches the ball he is on the other side. (00:04:30)
Continuity mistake: At graduation, while they are dancing, when Chad drops the basketball from under his arm Troy picks it up, but in the next shot Troy is not holding the basketball he is dancing with Gabriella.
Continuity mistake: When Troy and Chad are in the junkyard, Troy gets his hands dirty. In the next shot his hands are now clean.
Continuity mistake: When Troy and Gabriella are dancing on the rooftop, the potted trees and hanging potted plants are swaying in the wind in some shots but are motionless in other shots.
Continuity mistake: When Gabriella speaks out to everyone in front of the piano, to get them to agree to do the musical, in the first shot her hair is over both of her shoulders, then it is pulled back behind her right shoulder. In the next shot it is hanging in front of both her shoulders again.
Continuity mistake: During the rehearsal of "Just Wanna Be With You", Jimmie leaves the cup of paint and paintbrush beside the railing. Not only does the cup of paint move (note rail post and pickets) in following shots, but after Gabriella dabs paint on Troy, the paint cup just vanishes, as well as the paintbrush Gabriella dropped. (00:52:05)
Continuity mistake: When Troy and Gabriella are rehearsing "Just Wanna Be With you," Jimmie is seen painting in the background. In the first shot, Jimmie is crouching and gradually stands up. In the next shot, Jimmie is crouching again. (00:50:45)
Continuity mistake: When Troy surprises Gabriella at Stanford you can see that she has some dirt on her arm. As they continue to dance, you can see that her arm is clean.
Continuity mistake: During the outdoor graduation, the shadows on the lawn very noticeably change between shots.
Continuity mistake: Troy tells Gabriella he's never been to a dance, much less a prom, but the picture on his bedside table and the picture in Gabriella's locker in High School Musical 2 were supposed to have been taken at Junior Prom.
Continuity mistake: When Sharpay is on the phone with her parents you can see Troy in the background, but he's only supposed to make it for the second act.
Continuity mistake: During rehearsal, just after Ryan cracks up at the sight of Chad in the clown suit, as Taylor pulls Chad away Gabrielle walks to the center of the 'balcony', with her back to Troy. Next shot, however, Gabrielle is back near the corner or the railing facing Troy, but next shot she's farther away again. (00:51:50)
Visible crew/equipment: When Jimmie and Donny are talking backstage of the senior year show, you can see a crewmember reflected on the pink picture.
Continuity mistake: After Troy has the chat with Chad on the basketball court, when they're joined by Coach Bolton there is a close-up of Chad and Troy, whose graduation gowns/sashes are neat and tidy. Then after a shot of the coach as he tells them to get back to the stage, in the teenagers' next close-up their graduation gowns/sashes are all mussed up and disheveled.
Continuity mistake: In the scene where Chad asks Taylor to the prom, at the very beginning of the scene, a shot is shown that shows the whole cafeteria. Neither Chad nor Troy can be seen at the top of the railing. In the next shot, however, they are suddenly there.
Continuity mistake: When the students are complaining around the piano, depending on the shot Zeke either has his arms folded or suddenly has his hands in his pockets.
Answer: I think that they are just props. The owner of those jerseys has no relevence to the plot.. They might just be randomly picked names.