What cole was trying to say is, think of Universal as yourself for a second. You were born in 1990 and you turn 25 on June 7, 2015 - the day of your birth (or in this case, the day Universal opened).
So Universal's 25th Anniversary *technically* is from June 7th, 2015 up until they turn 26 next June 7th. That's the way Disneyland is celebrating their 60th this year. They started a tad early but are going all the way up until the 61st comes around next year.