If that email is correct, and they offered admission to 1470 EDI applicants to Boston, then that throws many of the above assumptions out the window. Assuming that there will be EDII admits, the Boston campus could see 1,600-1,800 admits for 2,600 spaces.
That would leave fewer than 1,000 admits left for Boston out of the RD round. I don’t think that anyone disagrees that Boston is well-publicized at being capped at 2,600 freshmen.
If there are 400 NU.in admits, then that leaves fewer than 600-700 NU.in admits left in the RD round.
This would be a ramp up in the number of applicants taken ED by a pretty big margin.
Assuming 1600 Boston ED admits, with a yield of 35% (again, most likely too low, but for our purposes, consevative), that means approximately 3,000 applicants out of the remaining 95,000 will be offfered a Boston spot.
With respect to NU.in and Mills, assuming that 500 of the 2,000 spots are taken EDI and EDII, that leaves 1,500 spots. With a combined yield of 15%, that would be 10,000 acceptances to fill the 1500 seats.
The overall acceptance rate would then be 2,000 acceptances EDI and EDII, plus 3,000 RD Boston acceptances, plus 10,000 NU.in/Mills acceptances, you have an acceptance rate of only 15% across all admission programs.
Keep in mind, this assumes a very low yield for NU.in, and assumes that NU.in is maxed out according to the publicized highest cohort of 1170 students. Since then, given the Boston campus bed availability issues, NU has been a more conservative in projecting space available.