Hello. The rationale for section 3.7 is that different formulations could cause products to have different properties. One should not assume that two product having different non-medicinal ingredients have identical properties. For example, they may have different pharmacokinetic and / or clinical properties.
Your second question is related to section 3.7 but also touches on other issues in critical appraisal. A clinical trial is an instrument designed to evaluate a hypothesis relating to that particular / precise independent variable. Just as you would not generate claims that extrapolate beyond the studied population, you should not generate claims that extrapolate beyond that independent variable.