Thanks for your comments. I believe that my model fell short in that I didn't adequately take into account the faster finish times this year. The BAA announcement describes a significant shift towards faster times in the 10-20 minute and 20+ minute margin buckets compared to last year. Consequently, the density of runners in the slower BQ regions was lower. I believe that this trend should and can be tracked going forward.

It is possible also that I under-estimated the number of international runners.

Others have wondered about the gender-age distributions also. That may take some time to sort out. I would typically want to do a deep dive into the entry list to work this out and that hasn't been released yet.

It is interesting that the BAA lowered the standard qual times for under 60 year olds but left them as is for the 60+ runners. This is likely due to there being so few of us older runners who want to be in Boston. It is as if next year the younger runners will be subsidizing the entry of the older generation - like Social Security extended into the world of running. I think that would be fun to quantify.