Thank you Vic.  I was too hasty to dismiss the possibility of a house style.
I checked a few pages and the loose lines I examined happened to contain
unconsolidated contractions, and the tight lines happened to have the
exceptions you noted (plus one error by a type-setter) and I was misled. I
should have recalled Henry James' troubles with the house styles of his
early magazine publishers.

P&P's antiquated speech presented some challenges to the house style
(thou'lt,  etc) and "Some Rambling Notes" in STW must have given that
compositor fits.

Still,  if you count the first ten letters backwards....

Kevin Mac Donnell
Austin TX