I never trust them either, if amazon added 100 listings it doesnt mean 100 games are coming soon, it is likely them just creating a batch of pages they can edit at a later date so they dont have to do all of it at that time.
I am sure some of them will be E3 games but others could be used for other events such as the Game awards.
I dont think Nintendo will tell anyone about what games they are releasing before they announce them, more so as no one can keep a secret which is shown by the pokemon direct leak in which some one leaked the whole direct and more for the latest pokemon direct 2 weeks before the direct.
Amazon and Gamestop both have listed 20+ games each I think they know enough and are getting ready to have pre-orders roaring to go as soon as the new games are announced. As far as what 1 new 3DS game do I think it coming? Huh not super sure Nintendo has been on a kick of release Gamecube games on the 3DS, so why not Mario Sunshine lol