Final answer:
The variant inventory quantity can indeed be returned through a product's storefront JSON endpoint, allowing for accurate inventory management in e-commerce platforms.
Step-by-step explanation:
The answer to the question, 'Variant inventory quantity can be returned in a product's storefront JSON endpoint?' is true. In the context of a storefront's application programming interface (API), specifically one that may be used in e-commerce platforms, the JSON endpoint can indeed return variant inventory quantities. This is because product variants, such as size or color, are an integral part of inventory management in online stores, and the API needs to provide comprehensive data, including quantities available for each variant, to ensure accurate and real-time inventory tracking.