420 is definitely not a funny number in the Netherlands. Except maybe with the permanently online or stoner crowd. I’ve never heard or seen a joke with 420 in the Netherlands. Most people wouldn’t even get what it means and more people would recognize 69 as a funny number than 420.
Well, I disagree because I do see it referenced to a lot. Sure it depends on the crowd but if you have never heard or seen someone joke with 420 then I think that's also quite exceptional.