The whole face, always
Brow hairs, pores, lid folds, lashes, iris fibres and the page in the cornea stay visible at rest in every era. Anything that hides the face may appear only inside a cut.
The rule
An era is a lens on the detail. It is never a replacement for it. Frost, blur, masks and fades are allowed while the eye is changing era, and nowhere else.
Why
Two designs died for hiding the face. One redrew 1970 in characters. The other gave 2013 a frosted sheet over the eye at rest, the way that year's interfaces blurred what was behind them.
show all the details like 1970, not removing all
The frost stayed. It moved into the cut: it lifts off as 2013 arrives and mists over as it leaves.
The test
Stop on any era and look for six things: a brow hair, a pore, the lid fold, one lash, an iris fibre, the page in the cornea. If one is missing, the era is not finished.