It went on for months, even if they outsourced a team that just happened to interpret its orders "creatively", having such a scam operate under your watch, while you're paying them, is--to put it mildy--quite the oversight.
You clearly have never worked with an outsourced team. Shit like this can happen with the utmost of ease - unless Google has an internal time constantly involved in the actual area of the outsourced team.
Months is an incredibly short period of time for a large organization. Especially when considering a small, probably low priority group. A large organization isn't like a startup, for a small low priority group the feedback loop isn't daily, its at best weekly and quite possibly longer even monthly (and gets longer as you go up the corporate ladder). What you may identify about a groups activities in a couple weeks at a small company can easily take months in a large company.