Couple of things found so far: I didn't have a "proper" spec for the file format when I wrote the converter (I do now!). I based it on the BGA version where all the elevations are in feet; I didn't take the units (ft or m) into account. Also, I didn't have a full list of types and said that any number 4 or more was landable, anything less not. This ties in with what you said, now I've seen the full list.
I can see a couple of problems with the handling of "codes".
Should be easy enough to fix, though I'm already making some changes in other areas too, which may delay things a bit.