This page contains various disorganized bits of information that I haven't put anywhere else yet.
Don Larsen, who pitched the only perfect World Series game (in 1956), apparently played with the Aberdeen Pheasants in 1947. (Source: page 98 of Allison Danzky and Joe Reichler. The History of Baseball: Its Great Players, Teams and Managers. Prentice-Hall, Inc. Englewood Cliffs, N.J. 1959.)
Neil J. Sullivan's book "The Minors" contains a paragraph on the earlier Northern League years. p. 169 says:
These leagues were often more than mere trivia for baseball fanatics. The Cooper-Country Soo League lasted but one season, but the following year it joined with the Northern League, a three-year-old circuit, to form the Northern Copper Country League. Calumet and Lake Linden combined with Duluth, Fargo, and Winnipeg from the Northern League to form the new circuit. The Northern Copper Country League lasted for two seasons before it was reorganized back into the Northern League in 1908. The League failed to finish that season, but returned in 1909, in an altered state, as the Minnesota-Wisconsin League. The Northern League reappeared in 1913 with part of the then-extinct Minnesota-Wisconsin League. The new Northern League operated as a Class-C circuit from 1913 to 1916. It collapsed in Class D during World War I and reappeared from 1933 through 1942, moving back to Class C in 1941. After suspending operations for World War II, the Northern League was part of Class C from 1946 through 1962, and then it moved to Class A from 1963 through 1971.
(Source: Neil J. Sullivan. The Minors: The Struggles and the Triumph of Baseball's Poor Relation from 1876 to the Present. St. Martin's Press. New York. 1990.) The "Cooper-Country Soo League" referred to by Sullivan is a typo; it should be "Copper-Country Soo League".