LOL I really don't know!
I've been using a generic cocoa butter from Shopper's Drug Mart, and pumping at very different times every day for .5 hr - 1 hr. Maybe the erratic pumping schedule keeps 'em guessing? I've been eating pretty healthy lately, too, lots of veggies and good fats and few carbs. I don't drink caffeine, I don't like coffee - maybe that helps because caffeine inhibits cell growth. But honestly, it could be any number of these things or none at all and just chance!
I have been good with making sure to pump every day though. Maybe that's it.