I looked into this and found the problem. I used the gmad extractor to look at the code in those files. It turns out that there are missing closing brackets in all of them.

"VertexlitGeneric"
{
"$basetexture" "models/GrandTheftAuto5/Trevor/upper_diff_010_a_uni"
"$bumpmap" "models/GrandTheftAuto5/Trevor/upper_norm_010_a_uni"
"$phong" "1"
"$phongboost" "0.05"
"$phongexponenttexture" "models/GrandTheftAuto5/Shared/phongexp"
"$phongalbedotint" "1"
"$phongfresnelranges" "[.5 .5 .5]"
"$model" "1"


// ------------------------------------------------------------------------
// PLAYER COLOR CUSTOMIZATION
// ------------------------------------------------------------------------

// The following chain of proxies is to modulate phong tint (and rimlight,
// by extension) according to your chosen player color, but only within a
// certain saturation range: 50%. This might be confusing, I tried my best
// to comment it, e-mail maxofs2d@facepunchstudios.com if you have any
// questions regarding how player colourability is set up in VMTs. GLHF.

"$blendtintbybasealpha" "1" // alpha channel of $basetexture: color mask.
"$blendtintcoloroverbase" "0" // blend mode. anything =/= 0 is ugly!

// --- Test values. Comment the PlayerColor proxy to use one of these.
// "$color2" "{0 0 0}" // Black
// "$color2" "{255 0 0}" // Blue (default)
// "$color2" "{59 121 160}" // Blue (TF2)
// "$color2" "{180 52 41}" // Red (TF2)
// "$color2" "{100 72 58}" // Brown
// "$color2" "{140 208 112}" // Green
// "$color2" "{248 166 202}" // Pink
// "$color2" "{160 100 140}" // Purple
// "$color2" "{242 168 96}" // Yellow (gold-ish)

"$PhongBrightnessScalar" "0.5" // see below. "0.5" will get overwritten.

Proxies
{
PlayerColor
{
resultVar $color2 // pass the player color value to Gmod
default 0.23 0.35 0.41 // unused for now.
}
Clamp // clamp the chosen color between 1% and 125% (usually)
{
min 0.01
max 1.25
srcVar1 "$color2"
resultVar "$color2"
}
Clamp // copy this value to phong tint, clamp it to 50% min.
{
min 0.5
max 1.0
srcVar1 "$color2"
resultVar "$phongtint"
}
Equals // copy $color2 value to exterior variable. this makes it
{ // no longer a RGB array but a single float instead (!??)
srcVar1 "$color2"
resultVar "$PhongBrightnessScalar"
}
Multiply // multiply $phongtint by this new float value.
{
srcVar1 "$phongtint"
srcVar2 "$phongBrightnessScalar"
resultVar "$phongtint"
}
Clamp // the result of this multiply doesn't go any lower than 20%
{
min 0.25
max 1.00
srcVar1 "$phongtint"
resultVar "$phongtint"
}
}
} <-------THIS IS MISSING IN ALL OF THE SHIRT.VMT FILES

AUTHORS: I suggest you fix this.

I am waiting too!