When used in forensic investigations, facial reconstruction is actually a last resort, specifically because of the limitations inherent in the technique.
Skeletal remains provide only hard tissue. From there, the forensic artist has to determine specific anatomy landmarks where muscles attach and work from a limited pool of data regarding how deep the tissue is in those spots according to gender, age, and race.
That opens a fairly wide range of possibilities right there. Then it’s up to the artist to determine skin tone, eye color, and hair color. Other areas completely open to speculation include wrinkles, birth marks, skin folds, how much fat tissue was present, the size and shape of the ears, and whether the earlobe was attached or free.
There’s also no telling what kind of hair style the person had, if they wore make up or glasses, had a facial tattoo or if there was some other noteworthy, ephemeral characteristic that a witness would see, but no record remained of in the hard tissue.