It does make "sense". Processing newer applications first keeps the official processing time (which is the time it takes to process 85% of applications) lower., which reflects well I guess. But nobody knows more about the 15%. What is the average processing time of the 15%? Minimum time? Maximum time? Still processing 5 years later? Nobody knows, because those data don't get reported.
As for myself, I can't decide whether to contact them or not. Been 7 months since my last update (test completed). On one hand, I feel I still need to be patient, I won't reach that 21 months until November. On the other hand, what if something did go wrong?