Tim Lloyd writes:

If you look at other Byzantine coins and icons, in particular, you frequently see the double-line, neckline of a garment on emperors, saints and particularly Jesus and the Virgin Mary.

Interestingly, the Christ Pantocrator icon from St. Catherine’s Monastery in the Sinai, shows something that seems like the double line as shadowing on the neck well above the garment neckline.

I think you are pushing it too far to consider the double-line neckline as evidence of the source.

In a back and forth we agreed that you can’t rule it out any more than you can rule it in.