Let's get a bit deeper into those amiibo numbers
Amiibo shipment WW up to December 31st, 2014 - 5,700,000
Amiibo shipment in US + Canada up to December 31st, 2014 (63% of overall) - 3,591,000
This is a pie chart indicating the regional shipment breakdown of amiibo from its launch until the sixth week of this calendar year.
As you can see at a glance, the sector in red representing the U.S. and Canada accounts for a significant portion: 63 percent. The sell-through proportion of the total shipment is approximately 70 percent in each of Japan, U.S. and Canada, and Europe while it reaches 90 percent in Australia
Amiibo sell-through in US + Canada up to December 31st, 2014 - 2,513,700
Hypotesis (backed by older data): Split between US and Canada for sales: 90% - 10%
Amiibo (hypotetical) sell-through in US up to December 31st, 2014 - 2,262,330
Amiibo sell-through in US up to February 28th, 2014 - 3,500,000
Amiibo (hypotetical) sell-through in US in Jan-Feb - 1,237,670