It should be noted that pAg is meaningless if taken of a solution of Silver Nitrate as pAg must be in reference to something else! In this case it is halide. So, the initial pAg is taken of the HALIDE solution in the kettle and then is continued as Silver Nitrate is added.
Ammonia has a profound effect on vAg, but as of the last time I worked on the model there was no model for this effect which worked properly. Since SRADs were no longer made at EK, this was a moot point. Other methods were in use since the 70s or earlier.