From 1924 to 1928, he published his famous key papers on AV dissociation and heart block.
But in terms of fundamental understanding, a key paper remains that of Thomas Gold more than half a century ago (Gold 1948).
This was followed by a key paper in the British Medical Journal and a book of the same name.
The key paper that came out of Cass's and Karl's discussions was the "Do sunspots matter?"
This is one of the key papers on singular integral operators.
But that may not be possible if you don't have a few key legal papers.
Besides, two of the key papers are weeklies.
Some key papers in the development of NPR are:
He published a key paper in 1859, and later a book on the subject.
A key early paper was written in 1969 by Chauncey Starr.