How many chickens are being saved by corporate campaigns?

Please correct me if I'm being silly, but I was looking to evaluate animal advocacy against corporate campaigns and came up with an estimate far lower than Open Philanthropy's one (at least 2 orders of magnitude lower).

I then reviewed their work and found a very odd set of logic. Open Phil claims

At any time, about 265 million U.S. egg-laying hens are confined in microwave oven-sized cages

But then later claims:

Counting just the ~$2.5 million spent on corporate cage-free campaigning over the last few years, and conservatively assuming that the campaigns only accelerated pledges by five years, these campaigns will spare about 250 hens a year of cage confinement per dollar spent.

That seems to imply that the intervention would save $2500000\times 250=625000000$ hens. But that's 2 and a half times the number of hens even in confinement! Have I made an error? What assumptions am I missing?