Dear Charles, Dieudonné and Grothendieck themselves changed their terminology in the second edition of EGA I, published by Springer Verlag in 1971. At the end of their Avant-propos, on page 3, they write:
Signalons enfin, par rapport à la première édition, un changement important de terminologie: le mot schéma désigne maintenant ce qui était appelé "préschéma" dans la première édition, et les mots "schéma séparé" ce qui était appelé "schéma".
As to the suggestion "it was discovered that there were far more propositions about preschemes than about schemes, and people decided that this was ridiculous": considering the God-like status of Grothendieck and the awe he inspired, this sounds to me as plausible as courtesans telling Louis XIV "hey, this royalty business is pretty ridiculous. Why not name our country The Democratic Libertarian Republic of France?"
Euclid's Elements of Geometry (1482)
In the 1455 Gutenberg bible the illustrations were hand-drawn after printing.The illustrations in the 1482 Elements were printed. [In some copies the diagrams were colored in by hand, see right image above.]
In a foreword the printer Erhard Ratdolt attributed the prior lack of printed mathematical works to the difficulty produced by the diagrams, and adds "Having perceived, that it was this alone that formed an obstacle to something that would be useful to all, I have achieved, by applying myself to the problem and not without putting in much hard work, that geometrical figures can be composed with the same ease as movable type".
There appears to be some uncertainty on the nature of Ratdolt's method, which he did not explain any further. The common practice in the 15th century was to use woodcuts for illustrations, as discussed by Bowers. Alternatively, according to this source, Ratdolt had devised elementary geometrical forms in type metal which could be combined to form figures which, being in metal, could be printed at the same time as the typeset page.
The OP asks also for early printed formulas. The earliest appearance of + and - symbols appears to be Johannes Widmann (1489), see image below. Notation that would need subscript or superscripts (such as exponents) was generally avoided, as were fractions with a bar. A quote: The bar is generally found in Latin manuscripts of the late Middle Ages, but when printing was introduced it was frequently omitted, doubtless owing to typographical difficulties. This inference is confirmed by such books as Rudolff's Kunstliche rechnung (1526), where the bar is omitted in all ordinary fractions but is inserted in fractions printed in larger type and those having large numbers.
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All these young people talking about being old! I paid a secretary through the nose to type my thesis in 1964, doing much of it myself, and using carbon paper to get a copy. Lots of handwritten graphs of spectral sequences. The memory of that horrid process may be one reason I never published my thesis. It is roughly 150 pages of dense calculations.
At Chicago in the 1960's and 1970's we had a technical typist who got to the point that he, knowing no mathematics, could and did catch mathematical mistakes just from the look of things. He also considered himself an artist, and it was a real battle to get things the way you and not he wanted them.
My collaborators and I published five long Springer Lecture Notes in Mathematics volumes between 1972 and 1986, and all are cluttered with hand written symbols, although the Selectric decreased the number in the last of them. The first of them (in which I introduced operads) is especially painful reading now.
Somebody on this thread mentioned translations by non-mathematicians. I could never find it again, but I once read a paper about CW complexes that was translated from a Chinese original. It talked about the $n$th bag of bones.