Thanks @Luke_C. I've seen this (and run it!) previously. But useful pointer for anybody who hasn't found it.
This is a useful workflow, but not as handy as a flag next to the actual challenge (and index). So we can instantly spot the gaps rather than cross-referencing. In the same way as I can immediately see which interactive lessons I've completed.
Just an idea - to make an already brilliant resource even easier to navigate! Presumably it must be possible (perhaps straight forward?) to implement as we can already see who the last person to post was, so somewhere it is recording everyone who posts. So it just needs something to check whether the current user has ever posted on the thread. (Assume anybody who posts has completed the challenge - fair assumption for 99.9% of people I reckon)
