There's plenty of evidence to suggest there was some stockpiling, even from Nintendo sources. Consider that they sold 350k Wiis on Black Friday week in USA alone, and Reggie said that the 600k in one week record would be beaten again.
1.8 million units per month is ~414k units per week. Look at that number, then look at all the numbers from various sources and ask yourself if it's in any way possible that they are not stockpiling. I believe it's not.
Regarding when 1.8 million per month production started, it was during fiscal Q2, which takes us back to the end of September if not earlier.
Sources:
http://www.bloomberg.com/apps/news?pid=20601101&sid=a3FKYMLPMdoE
http://kotaku.com/gaming/black-friday/nintendo-350k-wii-sold-last-week-record-ds-sales-327167.php
My Mario Kart Wii friend code: 2707-1866-0957
