The five weeks after the first for AC sales were around 1.7m if you look at the weekly Japanese sales and compare them to the five week total after the first it shows at this point the majority of sales are coming from that one region as it's like 300k a week which we know from Famitsu estimates is what it has been selling in Japan. This suggests that with WW regions ACNH may have been a lot more front loaded compared to prior games in the series which poses the possibility of the game's legs being a lot more dependent on Japan in the long run than thought.
In comparison SW/SH shipped more but the added shipments in the quarter suggests the 16m has now been sold through, the game was the second best selling non new release after MK8D despite people suggesting that it was dropping off in the charts quicker than expected. In Japan it still sold 310K in the quarter meaning WW regions it did 1m showing it's legs are more across different regions in comparison which could make things difficult in the long run for ACNH to close the 4m gap as it's seemingly falls on Japan at this point.
You're comparing apples to oranges here. The 11.7M as of March 31 was worldwide shipped (aka sell-in). The 13.4M as of now is sell-through to customers, and only in JP/NA/EU. So the total worldwide shipped now is quite a bit more than 13.4M.