Yes, I confess that the sales reporting features of Market are fairly simplistic.
As time goes on, this is an area that deserves improvement, so it will be addressed down the road.
At the current time however, it is what it is.
For what you're doing, you may be able to utilize the "inventory control" feature. You could just set all of the inventory levels at a high starting number like "1000". Then, as each one is sold, the number will decrease — and you can see how many of each were sold. (start with a high number, so you don't sell-out)
Inventory levels ARE shown on the Market Theme sales reporting page, so that could actually work for your purposes.
At the end of the year, you simply subtract from your starting point to see how many you sold. And then you can reset the starting point back to the initial level.
Hope this helps.