[H3N51N]

Because 2015 is 02's anniversary. Adventure & 02 are the same timeline & universe. You can't do a season with the Adventure kids being 17-or-so without acknowledging 02's events since it's gonna take place after 02. And the more I think about it the more I believe this was intentional. Imagine if we had the celebratory season last year with just Adventure & then this year would've been the one with 02.....only the Adventure cast is 2/3 of the 02 cast. Meaning the Adventure people would technically have 2 specials in a row which would be repetitive & exhausting.