I was mainly directing you to that single point you made.
That new IP's tend to be frontloaded. Yes, that can be very true... if the game only serviced a small niche, or if it didn't hit like it could have. Then you have those new IP's that shape not only the console they released on, but to degrees the entire market. CoD, Gears, Halo, and the Wii "" line are some to look at.
Popularity, word of mouth, signifies how frontloaded a games sales will be. And that's nothing you can get from it's first month of sales. Hell, even second and third month can hide an emerging trend.
You may be completely right about Splatoon. But it's first "month" of sales (in this case two days) won't tell you anymore than what it did in those first two days. And you can try to read tea leaves from sites like Amazon, but that's a crapshoot. Don't stake everything on it.
Most of all, have fun. NPD is our own personal monthly soap opera. That we get to influence. Some of us add wit, some add fact, some add wild speculation. At the end, hopefully, it is an interesting dramatic reading reflection of the current market. And probably not something to be proud of, but definitely something to marvel at.