Example.
Last Week I made Adobong Manok Sa Gata or what is known as Filipino Chicken in Coconut Milk. When I went to select chicken thighs, I knew I wanted some with medium amount of fat content as I was going to use the fat for a braising liquid, but I did not want too much fat as the Coconut Milk has more than enough and wanted the Coconut flavor to come through more pronounced.
I spent a long time going through Chicken Thighs to find some that were not as fatty as usual with about 1/16 or so uniform thickness of fat cap with no gobs. Sure, the label reads the same as the ones I rifled through, but the fat content was incredibly different as was the protein content between all of them and the ones I selected.
Going by the label, you would think they would be the same, but they sure aren`t. Anybody with eyes can see that. Unless you are weighing it all and sending it to a lab to get analyzed, you have no idea of the actual amino profile. You only have an estimate. Not that this is a bad thing, but thats what you have, an estimate with no clue as to the specific amino profile.