When, and why, did the word ‘sure’ become so ubiquitous at the start of answering a question?

I’d like to thank my wife for arranging access for me to the State Library of Victoria (for free!) Inter alia, this gets me access to the OED.

OED?

First attested use: 1651, in a trial transcript:

Att. Gen. Was Mr. Love present when this letter was read? Far. Yes sure, he was present.

First instance in their list without a yes or aye, with sure at the start: 1914:

P. G. Wodehouse Man Upstairs 133 ‘Is that a fact?’ ‘Sure,’ murmured Archibald.

Then 1963:

Mrs. L. B. Johnson White House Diary 26 Nov. (1970) 11 If it had been a request to chop off one’s right hand one would have said, ‘Sure’.

The sarcastic sure example they give (“orig. N. Amer”) is earlier, 1907:

L. Scott To him that Hath iii. ix. 250 Just then her hand happened to fall on mine—accident, oh, sure!

OED does say that it is “chiefly N. Amer. in later use”.

So: popularisation was American, and probably the ’60s; but if P.G. Wodehouse used it, then America is not where it came from.