A fascinating question.
A bit of searching unearths this masters thesis
Which says about the incident:
This account intimates that Molly became a dairy maid, work at which she labored until approximately the year 1683 when she was accused of pilfering a bucket of milk and was ...
Since you use Genesis 38:9 as the foundation for your hypothesis, please know that Onan's death was the result of spilling seed (having sex but spilling his seed outside of her vagina) in order to prevent his wife (his brother's widow) from becoming pregnant. He did this out of greed, to derail his Levitical duty to give her offspring, and thus deprive her ...
The association of the phrase "spilled milk" with Benjamin Bannaker's grandmother occurred much later than the 1600s.
The first account of Bannaker's grandparents (Memoir of Benjamin Banneker 1845) says:
His father was a native African, and his mother the child of natives of Africa; so that to no admixture of the blood of the white man was he ...
Are there any grammatical or historical reasons why thoroughty could not have functioned just as well as thoroughness?
There is no reason that I know of that makes it so that -ty necessarily could not have functioned to form a noun thoroughty with the same meaning as the actually existing existing thoroughness. I only mean this in the very weak sense that ...
Raze, from vulgar Latin rasare, meaning "scrape, erase." 15th or 16th century.
Raise is of Germanic origin, and three or four centuries older: risan.