Just got done watching Into Darkness on Blu Ray and notices some things about the undershirts...
First, it looks like the "Khan" style undershirt with the mock turtleneck is only worn without the tunic. Any time an actor is wearing the tunic, they are either wearing the first movie style undershirt, or a variation that has a slightly taller neckline with a zipper in the back.
My assumption is that the costume designer liked the height of the mock turtle neck shirt, but did not like the seam line, so a variation was made.
In any case, owning both versions of the Anovos undershirt, I have to say the "Khan" style fits over your head better, but you have a little slack in the back so it does not fit as snug and uniform as the 09 version. It looks to have a pleasing height because of the mock turtle neck BUT you get that seam line which is not present in the movie.
The 09 version on the other hand also looks very good when worn with the tunic (though I don't like the low-sloping yoke seam when worn by itself), I find that if I make sure the shirt is straightened and the collar adjusted anytime I get up from sitting down, everything looks really good.
I kinda wish I could have a version that is a combination of the two - I love the cuffs on the 09 version, but would want it without the sloping seam line like on the Into Darkness version.
Ahhh well, such is our hobby....we shall never be happy lol