My current estimate of sales is 3,660.
Since my last update blocks R28 and R29 have appeared on the website for selection (adding just over 300 to the estimate).
There was a sizable jump on 1 June (which is when those blocks 'opened') and that's probably related to people wanting to align their subscription with the start of the month.
Feels like we're heading towards 5,000-6,000 sales by the renewal deadline right now.