"Since I'm a U.S. collector of Canadian cents, I'm a little confused. I have to say that "retained broken die" actually sounds more accurate, since it is part of the die that is "retained" and the "cud" or "retained cud" is what appears on the coin as a result."
I would agree with this statement.
I have always believed that a cud is the result of a broken die and created when the coin is struck.
If the broken die is retained then there is no cud produced once the retained portion shifts enough and moves to a different level then the rest of the die then a cud will be produced.
To me the term retained cud doesn't make any sense and is misleading to what actually happens, you can retain a broken die in a position to create a cud or the piece can be dislodged completely and produce a cud but I would never call either a retained cud.
Just my opinion.