I you look at the Brow there seems to be an exsisting contour that does not match the finished eye / cheek bone orientation. There also seems to be a previous neck line behind the neck just intersecting at the Diadem straps. The depth of the neckline is considerable - as is the forehead - and jaw line. I believe this is how the engraver got past the majority of the previous features. The Lettering that is ghost throughout will help as well as the beaded tips of the font. Note the I in VESPASIANUS The odd nature of the Letters in AUG The Nose looks a little like Tiberius to me......
It looks like a modified bust of Otho. All the engraver did was pull the back of the jaw down to square it out and lengthen the nose.
Total no detail, this can beter. i like a coin you can see his life not perfect, they are older then me hehe