Looks to be right to me...
Dec was by far my best month (as it always has been the last couple years on Amazon and other vendors). Jan sales fell from that, and Feb a little more than that, but that's to be expected. Dec is almost always going to be the best month of the year.
B&N did send out an email that returns were being counted as sales for a little while there, so your reported returns were probably less than they actually were for Dec and part of Jan.
Jan sales do seem to be 100% for me. All of my test transactions go through almost instantly and my sales here are on par with other vendors.
My January sales are four times what my December sales were. February is trending to decrease by 20% which I expected once people used their gift cards and loaded their Christmas ereader gifts. But I don't see anything in my numbers, anyway, that causes me to be concerned.