Negotiable Maximum Population
'Negotiable' implies that this population is not fixed and can change as the requirements change. It is the 'maximum' because by definition the inclusivity of the product is unlikely to exceed that of the requirements specification.
This is not immediately obvious, but arises from the difference between the likely method of assessing the requirements specification and that of assessing the product. Any assessment of the requirements is likely to focus on the individual components in isolation, because the interaction between elements will be unknown and consequently not quantifiable.
This can be thought of as an idealised assessment of the best possible product to meet those requirements. In practice, though, any attempt to design an actual product to those requirements will inevitable involve some trade-offs that will reduce the inclusivity of the product. As the design process progresses, concepts and prototypes will be developed. As soon as anything physically tangible is produced, it can be assessed. This means that at any stage from initial concept through to the final design solution, the inclusivity of the product can be assessed from the physical properties of the prototypes. The people who could actually use the product, based on its physical properties, are referred to as the included population.