[polarized]

It was a deliberate design decision as the issue was mitigated in a different manner starting in early 2016 (and introducing that check wouldn't be very effective anyway for other reasons).

The results of the mitigation are shown in the paper as Figure 5. The success of the techniques in the paper decline rapidly over the course of 2016 and would effectively reach zero if the dataset were extended (this is noted in the text when it states that RingCT transactions are immune, although even without RingCT it would still effectively reach zero)