Personally, I consider all Wario games as having happened in universe, but I can at least see why some people might deliberately ignore a few of them. Like say, Wario Master of Disguise or even Wario Land Shake It.
But how about you? Any Wario games you consider as stricken from your personal canon?
Of course, all the games happened. In-universe at least. How else can other characters tell about them. Wario might lie sometimes, but his adventures are true.
(Or are they? That's up for you to decide.)
WarioWare is pretty in-character for Wario. He sees a money-making opportunity, and exploits the mindless masses for profit. I see no reason why he can't do that alongside treasure hunting. It's not like game developers don't have rest periods.
That said, Wario Blast probably didn't happen, based on its premise. Although stranger things have happened to him, I guess. Getting sucked into a music box is pretty weird. Could still be a thing. And like Just a Wario Fan said, he could just be embellishing in his recounting of adventures, or simply making it up.
