Let’s see if I can back-of-the-envelope this.
It looks like disadvantaged students were about 14.3% of their applicant pool. Then it looks like about 5/16th of those would fit into the 1400-1490 sort of range, which is about 4.5%. It looks like around 40% of those did not submit scores, so 1.8%.
Of course possibly this policy will induce more such people to apply, but still even then I would guess you are looking on the order of about 2% of their applicant pool.
And then the admissions odds were being multiplied, but still only being increased by a small amount gross–maybe around 4% for the whole of that range on average. So the marginal effect in terms of new admits would be something like 0.08% of the application pool. Application pool of say 28000, you are talking on the order of 20-25 different admits they are looking to get, around 1.2% of their admit pool.
Obviously this is a crude estimate, but hopefully that’s not a bad guesstimate for our purposes. Meaningful of course for those people, probably at least somewhat helping Dartmouth achieve its socioeconomic diversity goals, but not likely to completely change the composition of Dartmouth.