The only one I heard about was by Margaret Mitchell (Gone With the Wind). I expect there were others, but the syndicate caved on that one and Capp had to cut the arc short.
Odds are they’ll never run the Gone With the Wind parody but there’s a whole mess of stuff outside of that that doesn’t seem like it should have any copyright issues.
There’s a magnify button on the strip (hover your mouse over the middle of the strip). Sometimes it works, but not always, particularly on the early strips.
We won’t see it of course, but Abner is prescient here. Anyone know if Capp cheated on the count?