Just for the record, St. Demetrius of Thessaloniki, was not a Bishop.
As an officer in the Roman army under the command of Tetrarch (and then Emperor) Galerius Maximian , Demetrius became a Christian and imprisoned in Thessaloniki in 303, when Diocletian was emperor. According to tradition, from the prison he blessed his disciple Nestor to defeat the heathen wrestler Lyaio. The victory of Nestor enraged Maximian who was present in stage. So, St Nestor was beheaded, and St Demetrius murdered with a spear. They are both Christian martyrs.
St Demetrius is also patron saint of city of Thessaloniki.
Lakis, in my post, the link is preceded by the location of the icon, its approximate date and then a description. That icon is from St. Demetrios in Thessaloniki. It's an icon of St. Demetrios, but on one side is the Bishop of Thessaloniki.
The early depictions of Christ as a beardless shepherd ought not to be taken as icons in the sense that that was subsequently understood. They are not portraits of Christ but symbolical images. Initially, it is likely that images were made to conform to the expectations of the people of the Greco-Roman world of the first and second centuries. To say, though, that Orthodox bishops, indeed priests as well, did not have long hair until after 1453 does not seem at all right, and one can certainly see icons of the time of St Sergius and before of Russian saints which indicate this. Olga, however, will no doubt answer for herself.
Yes, sadly, iconoclasm was effective. You even go into Hagia Sophia, and there are iconoclastic crosses on the ceilings, and the mosaics you see are all after iconoclasm.
Actually, if you look at all the images I posted, not all are of Christ as the Good Shepherd. He was universally depicted with no beard and short hair.