The subplot about Dr. Wily being Dr. Light's old assistant and turning on him only exists in the American version. In the Japanese version, Wily was just a random mad scientist who had no initial connections to Dr. Light prior to stealing and reprogramming his robots.
The only version to keep score.
Even though Roll appears in the ending, her name isn't given in an American game until Mega Man III (NES).
The game takes place in 2008.
In Korea, Rockman was once known as "Mecha-Man" to avoid lawsuits with the creators of a 1970s Korean TV show that was named "Rockman". But later, eventually, most versions released throughout Asia all became known as Rockman, because that title was more well known than "Mecha-Man" or "Mega Man".