Once you cut that bone out of the center, you have two breasts.

Simply go by weight. 1oz cooked boneless skinless chicken breast is 9g protein.

Any labels that give macro counts based on one whole breast is going to be inaccurate because not all breasts weigh the same amount. And depending on whether it's been injected with any solutions will change the raw to cooked weight ratios (water and sodium are the most common injections simply for preservation processes). Also, cooking methods can alter raw to cooked weight ratios as well as macros (ie, frying vs griling).