If you Google the phrases "mark twain" and "oxford English dictionary"
it turns up a cached page from the Oxford English Dictionary that
states MT is "the 145th most frequently quoted source in the OED, with
a total of 2390 quotations (about 0.07% of all OED quotations)."
Total number of quotations: 2390
Quotations providing first evidence of a word: 75
Quotations providing first evidence of a particular meaning: 513
That MT is the 145th most quoted source is less interesting than the
latter 2 statistics, which reveal the linguistic innovation that you
have asked about. OED requires access by subscription that you could
get via your library. When logged in you will be able to click to find
the actual words and usages. I wonder if it would also rank MT's
latter two statistics with respect to other authors, as it would be
interesting to know how he compares to other innovators.
Source of above info is:
(Who knows how well or for how long the link will work!)
Hope you have a great day