Summary:
We follow the רוב by איסורים in general (but never by ממון) even against a חזקה, but not by איסור א"א. We cannot derive איסור (where there is the concern of לעז) from ממון (where such a concern does not exist). The חשש of ב' יב"ש is only מדרבנן.
A Simpfoin, which has witnesses on it; should be authenticated by its signatories - סמפון שיש עליו עדים יתקיים בחותמיו
Summary:
We know that the ברייתא is discussing where the receipt is ביד המלוה, since it is referred to as סימפון (not as שובר), and also ביד הלוה there would be no חידוש.