Eng 6012 inexists sp

No, it was more a note to myself at the beginning not to forget this case. Currently this shouldn't happen because by the time the resolveColumnIndexes/resolveColumnIndexesUsingSchema methods are called (after the best plans are built), all parent (grand-parent) TVEs in a subquery are substituted with corresponded PVEs, and the TVE themselves are moved up to the parent statements/nodes. 
Removed the comment.

I have a general question though. Should an exception be thrown if a column index can be resolved (set to -1)? Right now it simply return -1 and this is not discovered until the execution time when the EE throws run time exception