In regards to the FRC Blog post:
Helping Rookie Teams
Here is a chart comparing rookie registration over the same period to date in 2013, 2014, and 2015.
Note some of the data is interpolated and that's the unnaturally straight parts.
The start day for each year was one day off of the year before, so that was normalized to a common start date (this year's).
2014 had an unusually high initial registration for rookies for some reason.