Thanks - I am genuinly keen to help improve the map . I have hit exactly that scenario you describe.  The MapRoulette task shows a sequence of rare values for surfaces - most of which are typos or obvious mistakes and then you encounter a value which could be a mistake, or missing something and its so hard to tell, especially whne in the headspace that most previous entries were errors.
I'm pleased the other changes have been useful (As i hoped).