Korvin, those first four would all fall under "a container of liquid". For the last, obviously you could make a pearl, but the relevant question there would be whether you can sell it.

Darth Credence, some of them seem easy to me (like, I definitely wouldn't allow someone to cast Raise Dead with a conjured diamond, even though the strict RAW would seem to allow it), but others I'm much less sure about. Like, the key that the wizard saw hanging on the guard's belt: There's an argument that the wizard can't remember it well enough, but there's also an argument that it must take the exact form of an object the wizard's seen, so they can't get it a little wrong even if they try.

Or take the illusion question: On the one hand, if you can make something you've only seen an illusion of, that allows you to make an object that never actually existed. But if you can't, then it turns the ability into an illusion-detector. Neither one of those seems entirely within the intent of the ability.

I think the primary reason for "that you have seen" is to prevent people from making smartphones or laser pistols or the like (because you know that someone would try that). But it also gets to a question of how the ability actually works: Are you conjuring the metaphysical essence of a specific existing object, or are you crafting it yourself out of magically-conjured material?