"Of course, there is no such word"

I'm stealing this paragraph from Michael Quinion's 591st World Wide Words newsletter just because it's the kind of thing I find heartwarming:

[A reader] wrote, "I note your use of 'unseasonably' last week. Of course, there is no such word, even though it's used nearly exclusively when 'unseasonally' is meant. I'm wondering if you have a comment." I do. "Unseasonably" dates to the sixteenth century, while "unseasonally" is known only from 1941. Precedent alone makes my version correct. Style books I've consulted agree that "unseasonably" is correct the way I used it, based on their view that "seasonable" means "appropriate for the time of year" ("hot weather is seasonable for summer"), while "seasonal" means a thing occurring at or associated with a particular season ("the seasonal migration of geese").

Ahhhhhhhh.