Changes

a cow (Giotto)(Rublev)

angels (Pisano)(Giotto)(Rublev)(Coptic)

the Magi (Rublev)(Coptic)

the Light of the Holy Spirit (Rublev)(Coptic)

http://www.pravoslavieto.com/ikonopis/Gospodski/RH/

which attributes a nativity icon to the VII-IX centuries. I have identified its design elements in the above comparison as "Coptic". After looking at it and finding out that it is in the St Catherine Monastery I think that Rublev was influenced by Coptic work from the South. I imagine that some example of the Coptic art made its way to Italy to influence Pisano/Giotto.