Dan, You are right, but all the creases are almost impossible to do in such small resolution. There is a process with 3D sculpting (at least the one that works for me), that first establishes the volumes, then breaks the symmetry and increases the resolution.
You see, the creases are absolutely non-symetrical, so there is no point to make them in this stage. You correctly noticed that cheeks are sagging down towards mouth area, and the space between lower lip and the chin is wrongly shaped and that is my concern in this stage (volumes). The cheeks are looking wrong because I did not find the relation from the volumes of the cheek to the volumes of the mouth yet - that is what I'm trying to say
When I break the symmetry, I'll slightly break it for the volumes too, and then all the small creases and wrinkles will be added.
But before all that, person should be recognizable even in such small resolution and with symmetry enabled if the volumes are correct
Off course, there are people that are doing it completely different, like our friend Antonio Argudo here from PF.
He can in just few raw strokes get the relations between all of the main volumes, and almost instantly get the likeness (that is a talent I think...)
Unfortunately I do not have that skill, for me it is a process, few hours of fight against my own brain and it takes much, much longer
Still I hope I'll get there soon, and appreciate Your observations very much !