I wonder if we're (I'm) overthinking this now because there's implementation clouding the issue. Is there anything objectional about something like the following:
```
for subclass in subclasses
    If subclass hasattr _meta
        Subclass = get ancestor path

    If subclass in calculated subclasses
        Append to verified
    Else
        Raise an exception explaining
```
Apologies for the pseudo code, but GitHub's comment field is horrible on none desktop devices.

Doing it this way would eliminate the try catch, and thus could serve to remove the try method, and would mean the slice to depth thing is pointless too. It's readable, and simple from a maintenance POV too, I think.

The only cons I can see are clobbering the loop's subclass variable, and maybe accidentally letting other options I having classes through as valid input which would hit the exception case anyway.