That's a pretty poor analysis of online stats to come to the conclusion that VGC sales numbers are MASSIVELY undertracked. In order to put "4x Halo 3 launch week online activity" and "65% higher than Halo 3's best concurrent online activity" into proper context you need to first know the Halo 3 numbers. Without knowing the Halo 3 numbers you can't conclude anything about possible Reach launch week sales.
Remember also that VGC is an estimate and a tolerance of 10% up or down on the actual reported number is perfectly acceptable. So an opening week of 4.4 million has a reasonable probability of being the true launch sales and it would be churlish of anyone to suggest that VGC did a poor job of estimating sales were that the case.
Number of unique users online for any period of time is a very poor indicator of game sales.
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