Linguistic dark matter

[Cohen, Gerald Leonard]

I'm puzzled.  I typed in "shyster" and see some limited use around 1800 and 1820.  But I know from my research  that the term originated in 1843 (I wrote two monographs on the term a while back) .  This is no doubt a basic question: How does one check to see what sources Google cites to back up its presentation of "shyster" being used earlier?
 
Any help would be much appreciated.
 
Gerald Cohen

------------------------------------------------------------
The American Dialect Society - http://www.americandialect.org