How precisely can the difference method determine the πNN coupling constant ?

The Coulomb-like backward peak of the np scattering differential cross section is due to one-pion exchange. Extrapolation to the pion pole of precise data should allow to obtain the value of the charged πNN coupling constant. This was classically attempted by the use of a smooth physical function, the Chew function, built from the cross section. To improve accuracy of such an extrapolation one has introduced a difference method. It consists of extrapolating the difference between the Chew function based on experimental data and that built from a model where the πNN coupling is exactly known. Here we cross-check to which precision can work this novel extrapolation method by applying it to differences between models and between data and models. With good reference models and for the 162 MeV np Uppsala single energy precise data with a normalisation error of 2.3 %, the value of the charged πNN coupling constant is obtained with an accuracy close to 1.8 %.