If the resultant cannot be accurately measured, it leads one to doubt the rest of the calculations, methodologies used in determination and validation of wing design, and understanding of principles.
Of the two major manufacturers, ones models the entire aircraft, while the other models wings and fuselage separately. Would one expect the same results?
With respect, I beg to differ. There is an enormous difference between measuring, let alone calculating, the flow well downstream of the wing with all the attendant uncertainties and random influences and designing a wing. I find it difficult to believe that the major manufacturers should be lacking in understanding of how their wings operate.
So far as the differences in their techniques are concerned, that is really a matter for them. At the end of the day it is their money that will be paid to the customer airlines if they don't meet their guarantees. There is in any case a lot more to the design of a wing than making theoretical calculations of its characteristics.