Obviously forza could be over tracked but the reverse is just as likely. All those people saying to sold less then 2 million got be on something.

Good reasoning OP. But I don't know, if it sold so much, why wouldn't MS brag more about it? Or even release some concrete numbers? I believe Halo 5 FW will be more like 2m than 4m.

From what I've seen, they didn't brag about 3, Reach or 4's numbers either when they launched. 

May be plausible, but I guess NPD should tell us quite a bit.

Interesting, never knew about it. And yeah, NPD will clear our minds since a big part of Halo sales come from the US.

if we also use titan fall #s to that which is the exclusive that didnt come out at launch it would put halo 5 at 3.1million.

2M? Not a chance it sold that loe. It sold too well in the US to be anywhere that. We had reports from the Walmart/Best Buy guy (abriel?) that Halo 5 was selling really really well. If it sold 4M+, why don't they just say? That's an impressive number. I really want to know the figure and still a bit skeptical it's 4M but I can't see it being lower than 2M

Because if it actually had, they wouldn't be using PR spin and over-specific records, they would just be pointing to the sales numbers directly.

My theory is that they are using attach rates for all games sales versus the current console sales figures, rather than attach rates for those games at their respective week one launches, which would put Forza 5's attach rate at 7.4%, meaning to beat Forza 5's attach rate the game only needs to sell more than 2.03m ish.

In the past Microsoft announced software sales revenue. If we had just the software revenue we could figure out a rough idea of sales but unfortunately we didn't get that info this time. Given Halo 3 did 300m in 7 days and was part of Microsofts PR back then we had an idea of how well it did. With software+hardware it becomes useless info.

Will npd clear things or muddle them further? If npd comes out n releases numbers and says 5 sold 1.5 million what then. People could say less than 2 million fw. But I could still argue it did around 2.7 million globally(500k digital in USA). We really need digital numbers.

I think it will clear things. If it sells 1.5m like you said, I think it will be common sense that it did 2.5m+ FW worldwide (with digital sales included).