There is an important difference between catholic/ protestant and orthodox christening.
In the first two dogmes the baby receives the onction and they just wet a little his head. He has his gown during the whole ceremony.
In orthodox baptism the baby has a full immersion into the water so they undress it totally. After this they dress it again and they but ti the baby completely new clothes offered by the Godfather/ Godmother. These clothes are normal outfits, small pants, blouse, tie, luttel dress and coatsn full ones. Nothing to do with the christening down with long skirt worn by both boys and girls.
This is a very important point. So I don't really see how the orthodox royal families could use an historical gown already used, as it has to be completely new. Maybe the Orthodox Royal families being influenced by the other RF they amended this point or the Godfather still offers new clothes bur looking like a christening gown.
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