Nah your numbers seem to be wrong .
This from 5 years ago http://www.eurogamer.net/articles/2012-06-05-god-of-war-series-has-sold-over-21-million-copies
2.7 for UC4's first week WW. should have clarified.
but if UC4 is supposedly over 8.7m already and GOWIII was only at 5.1m ww 2 years after release, why the big jump now? the numbers might be wrong. my bad if so.