Your itinerary is valid (caveat: I have not checked that there are direct flights for each of your segments)
And yes, you are getting the hang of this

Your 16th segment could be an extra flight segment in Asia, where you are currently using only 3 of your allowed 4 flight segments
or an extra flight segment in Nth America, where you are currently using only 4 of your allowed 6 flight segments
It cannot be used as an extra flight segment in Europe/Middle East because you are already using your allowed 4 flight segments
It can be used as a surface segment anywhere