The "Leaving of Liverpool" is a good example.

Lots of folks about New York will glare at you if you sing
"my darling when I think on thee (rhymes with "united we will
be") in the chorus. They'll go to great lengths to tell you
that "That's not the way Bill Doerflinger collected it from
Dick Maitland at Sailor's Snug Harbor in Staten Island..."

Then they'll shore that all up with the reasoning that "nobody
said thee by the time Maitland heard it from an old Liverpool
tar." These latter are clearly those who didn't have grandparents
from the West Midlands of England...or haven't been to Amish
country in the US. And--- anyone who read the King James Bible
in that era, saw plenty of "thee's".

C.F.: the common colloquialism that "All fishermen are liars,
except me and thee, and sometimes I doubt thee."

Another (IMHO rather silly) argument is that "rhyming wasn't
so important back then." Well, then how come the rest of the
song rhymes.

A great deal of work to justify singing a line that sounds
like crap, in the chorus yet and as the last word of same, yet.

The most likely scenario is that Maitland or his "source" (does
a source have a source?) either mis-sang it or mis-heard it.

Which to me is a good example of "trad singer alteration," since
the likelihood of the song surviving much longer in the "old
tradition" with that busted last line is about the same as it
having done so in the "new tradition."

Those who put the obvious rhyme back have probably restored the
song to the original, not altered it. On the other hand, Maitland
and/or his "source" were quite likely the source of what is,
if we use common sense, a "breakage."