What’s the meaning of the Greek expression: “We called Him John, but we did not see him yet”?

Contra Konstantinos Konstantinides, I’m assuming the expression intended is Ακόμα δεν τον είδαμε, Γιάννη τονε βγάλαμε “We have not seen him yet, (but) we have named him John.” It refers to jumping to conclusions, making premature moves—just as it would be premature to name a baby before it is actually born (in traditional society, with high mortality at childbirth).

Nikolaos Politis’ monumental catalogue of Greek proverbs remains unpublished past epsilon, but this proverb has made it: https://books.google.com.au/book…. Politis gives this interpretation and associates it with a just-so story. My translation:

Of those who anticipate things and foretell future plans, founded on uncertain and indefinite expectations. A fairy tale (related by Mr K.D. Papaioannidou of Sozopol) underlies this saying, belonging to the class of tales told among both our nation and others of foolish women lamenting future disasters for an as yet unborn child. The story is as follows:

There was once a man with two marriageable girls; and one day a matchmaker came and brought a groom for the eldest daughter. The matchmaker sent her to fetch him wine from the barrel. When she put her jug under the barrel, she pondered her wedding, and thought: I will get married, and I will have a child, and call him John. But then it occurred to her that she might die, and she started lamenting; and the wine kept running. After a long time had passed, the youngest daughter came to see what was going on. When she heard what her sister said, she too started lamenting her dear nephew; and the wine kept running. Then the father went down; and when he learned why they were delayed, he shook his head and said: He haven’t seen him yet, we’ve already called him John, and the wine’s running!

The corresponding ancient proverb seems to come from a similar source: the goat has not yet given birth, and the kid is playing on the roof.

Politis then gives a long list of equivalent proverbs in other languages:

• Albanian “the child is not yet born, but his cap has been bought”;
• Italian “he’s not yet born, but he’s been called Nick”; “she’s not yet pregnant but she’s been called a mother”; “she’s not yet born, and she’s being married off already”;
• Catalan “The father has not yet been born and his son is already jumping on the roof”
• Spanish “We don’t yet have a son and we’re naming him”; “The goat is not yet born and it’s already suckling the kid”; “The son is about to be born, and they’re already boiling his porridge”; “He’s not yet born and he’s already sneezing”
• Rumanian “We haven’t seen him but we’ve named him”
• English “Boil not the pap before the child is born”
• Norwegian “Don’t write the child down in the book before it is born”
• Russian “The son is not yet born and has been named”

No, I hadn’t heard of that English proverb either. But here it is: Better master to Call not. W.C. Hazlitt, comp. 1907. English Proverbs and Proverbial Phrases