Regarding qed and with apologies if all of this is well-known to you.
1) In the Two New Sciences (pub 1638) Galileo includes a latin text on
local motion in days 3 and 4. This text uses many expressions to close
Propositions, quod erat intentum, ergo patet propositum and qed. This
latin text is a version of a text that G had written many years earlier.
2) Spinoza's Ethics (1665), written "more geometrico" has qed exclusively.
3) Newton's Principia also has qed exclusively.
On the basis of these data points it appears that this phrase became
"standard" around the middle of the 17th c.
The Greek version of qed appears in the standard editions of Euclid
(Heiberg). I do not know if this is supported in the manuscripts...
David Reed