Valentinian II portraiture styles

[Victor]

I have noticed that on some of Valentinian II's coins, his bust looks more like his father. Valentinian is typically portrayed as older, heavier and thick-necked; while Valentinian II is usually shown as younger, thinner, with a thin neck. Coin A below is the typical style for Valentinian I. Coin B is Valentinian II, but looks more like coin A, rather than coin C, which is typical for Valentinian II.

I am wondering if the engravers of coin B even knew what Valentinian II  looked like. They may not have seen an official imperial bust of him as this coin was from Antioch and Valentinian II was a ruler in the West.