It may not be quite a solution, but I think I've got the answer: it must be adjustable.

I know this because when I first bought my VX in 99, I could shut the gas cap door without the key. It worked this way for several years, until I needed to get some rear end body work. Ever since I got it back from the shop, I've had to use the key. However, they did not swap any parts, so I'd be willing to bet if someone gets in there and fools around a bit, there is some play in the way the latch goes together and it can be adjusted in such a way that you can close the door without the key.