If I may, you're being way too literal to the original low-res sprites! Does Bleed's Scorpion look exactly like the original Scorpion and Sub-Zero images? No it doesn't because he added more detail to it, like the straps showing through on the shin-guards and the black outline on certain parts of the fabric.
Have some fun with advancing the designs for an HD display! Shang Tsung should have his goatee and Goro should have the spikes on his forehead like Tobias originally drew.
The reason the spikes probably didn't need to be added to the clay model originally is most likely because that small of a detail wouldn't matter with such a low resolution sprite anyhow or worse, they would've looked like a muddied blob of pixels on his forehead. You guys are trying to make this an HD enhancement of the original, where details like that will add so much to the characters!