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Well yeah, Ace Attorney is developed and published by Capcom; it's not a first-party title. But to date every main series and spinoff game originated on a Nintendo system; in fact, the original trilogy and Dual Destnies were the only games ported to non-Nintendo platforms. It is evident that the series is loyal to Nintendo.
And if every series that had an entry or two on a non-Nintendo system was deemed not a Nintendo series, then not just Hard Drop, but also Dragon Quest Wiki, would not be in the NIWA. And if you want to get super technical, founding member Bulbapedia wouldn't be either, on account of the Sega Pico and a couple arcade games.
Oh yes, and come to think of it, Mario and Zelda had those CD-i games, didn't they...