I believe the PWT meter comes reasonably close to the concentration of ionic silver without any correction.
The problem is that to verify and correlate the results involves having your CS tested and that runs around $400 per sample. Ideally you would check your brew and send it to the laboratory to see what you actually have. If you ran 10 - 20 samples you would have a pretty good idea of how close the PWT values are to actual silver content. Unfortunately, this process is a bit expensive.