Economies of scale can be both internal and external; internal economies are caused by factors within a single company, while external factors affect the entire industry. Investopedia / Mira ...

External diseconomies of scale can arise ... thinking that it can achieve economies of scale in perpetuity. For example, if a company has reduced the per-unit cost of its product each time it ...

Another distinction, not discussed in your text, is between mobile and immobile external economies of scale economies. This distinction can be traced at least as far back as Robinson (1931). In his ...