July 20th, 1978: "To Draw Your Cork" and other slang

I've been reading a lot of Georgette Heyer that I got from the State Library.  So far I've read Powder and Patch, The Black Moth, and Friday's Child.  They're not very improving, but I have learned a lot of 19th century slang.  I know what a "wisty castor" is and what "to draw your cork" means.  I even find myself using it.  

When Pete made an excuse for something he'd done yesterday I said "You're doing it much too brown", and I know what a "leveller" and "a bunch of five's" are-though that expression hasn't changed much 

To be mugged or to be robbed used to be "to be forked", but what puzzles me is how Georgette Heyer got to know all that slang.  In Friday's Child, she even uses thieves' cant.  It sounds authentic enough.  Her dialogue is always believable (which is more than I can say for Emile Loring-the only book I ever found so bad that I threw it away even though I had nothing else to read!  She must write with the O.E.D. at her side.