Hi Sebastian,

re:
> How can it be a joined surface but have naked edges?

In MoI something is called a "Joined surface" if it's an object made up of more than one face (and so joined together along some edges) but isn't a solid because it has some naked edges in it. If there are no naked edges it will be called a "solid" instead of just a "Joined surface".

- Michael

There are still some remaining doubled and tripled surfaces in those areas where you're seeing internal naked edges.

- Michael

I've attached one here that's closer yet, with more doubled and tripled surfaces removed. Still at least one area that looks like it will need some reconstruction though.

- Michael