Actually making a product[termed an actual reduction to practice] is not a prerequisite to filing a patent application
with claims directed to that product. It is sufficient that the application contains, as the author states, a written description of the product[i.e., the conception] as well as description that would enable a person of skill in the art to make and use that product[termed a constructive reduction to practice]. 35 USC 112 sets forth the requirements of a patent application.
Countless patented inventions were never actually constructed by the inventor(s) prior to the filing of a patent application
with claims directed to such inventions.