You can query Data Explorer for the list of
Also check out Database schema documentation for the public data dump and SEDE, which has similar information (although the list of post types seems to be a bit out of date at the moment).
The README should also be updated, but the way the data dump is being distributed is changing, so I'm not sure what impact that will have on how this kind of information is made available.
I found that sometimes there isn't an answer corresponding to the question's AcceptedAnswerId
The data dump does not contain deleted content, so presumably the corresponding answers were removed by the owner or through moderation. I guess the export process doesn't remove invalid
AcceptedAnswerId values, but I'm not sure that there's necessarily a reason it should.