It is a major plot point in Goblet of Fire that the Marauder's map identifies Bartemius Crouch Jr. as simply Bartemius Crouch; therefore leading to the confusion that Bartemius Crouch (Sr.) was the person searching Snape's office.
This has always bothered me a bit; surely the Marauder's map would be able to distinguish between two different people? If Barty Sr. and Barty Jr. were standing next to each other, would the map show Bartemius Crouch twice?
Are there other instances of the Marauder's Map not showing the complete truth that would make it seem more plausible that it can't distinguish between a Sr. and Jr.?