There are a couple of skirmish missions that give you VP under certain conditions, once those conditions are no longer being met, you lose those VP.

One that comes to mind is one of the two Han Solo map missions. I don't remember the precise wording, but essentially, It's something like, while you controll the sabacc table, you are considered to have X extra VP where X is equal to some tokens.

So let's say I have 0 points. I'm playing with Jabba.

I control the sabacc table, or whatever is granting me these considered points.

I now am considered to have 4 points.

Can I spend these points with Order Hit? I think I can, since I can trigger the game's win condition with these, why can't I spend them?

So I spend them, now I'm only considred to have 2 points.

The condition granting me these extra points now goes away.

Do I go back down to 0? Do I go to -2?

There might need to be some clarification as to how Jabba interracts with missions that grant you temporary points, even though these missions will likely not see tournament rotation ever.

I think I can, since I can trigger the game's win condition with these, why can't I spend them?

If you are considered to have VP for the purposes of the winning condition, it does not automatically mean you actually have them for other purposes.

I would expect those VP you are "considered to have" not be available for spending. Otherwise why not use just "have", (or "gain" and "lose")?

At least I know you can't have negative VP and you cannot spend VP if you don't have enough.

I'd have to agree with a1bert

Being considered to have is not the same as actually having...