I find those very early depictions very moving, very haunting.
By the 11-1200's Christ's beard was pretty much the accepted standard in the West.
Interestingly enough, Christians in E. Africa kept Christ clean-shaven for sometime after that. The depiction below from an Ethiopian Ms. is believed to be from the 1400's.
Iconographically, you can usually identify Christ regardless of the number of other persons depicted in a scene, as his halo typically has a cross inscribed; that will generally be unique to Christ and no other figure's halo / nimbus will bear the cross.