the reason the have you using over drive early and big bud late
well theres a couple reason
the overdrive has a small amount of nitrogen and the big bud has none so they've got it so your feeding less N in later flower.. which is fine but it complicates mixing and is most times unnecessary
the real reason is so they can sell more bottles
the more bottles they can separate the nute in the more they can charge you for there full product line
and lie to you about how this product makes your buds bigger when its all just hype to make money
its just like wellsfargo trying to get you to open more accounts even thou you don't have a lot of money.... the more account you open the more money they make in stock revenue because it cooks the books to look like growth when its really just dilution