I'm not sure what you mean by "two boxes" since I don't know what you are referring to.
If you got a 1099-B for a sale of stock then you enter the 1099-B. That's the mantra.
The broker, maybe, sent you all kinds of stuff, 1099-B's, "statements", etc. but what you want to focus on is the "1099-B."
Whatever sales you report should be adjusted to the correct basis. So if you report a sale for 34 shares and a sale for 16 shares then you need to correct the basis for both.
