Here is the story about the legitimacy of the cup.
If you see the Stanley Cup outside of Toronto, its the REAL Stanley Cup. The "fake" cup stays in Toronto 365 days a year as a display piece at the Hall of Fame. To my understanding, its an authentic replica in every way, but a replica nonetheless.
The Cup that was at Daley Plaza yesterday is the genuine article. That Cup travels 250+ days a year for display at various arenas, for the SC winning team members to have for a day, etc.
As years pass, rings on the cup get retired. The Hawks will have their names engraved at the bottom, but as the years pass, that ring will move from the bottom to the top with the top rings going into the hall of fame when space is needed for new winners.