If you are speaking about the display assembly it’s self, Apple has both contracted others to assemble the assembly for them as well as assemble the displays them selves.
The iFixit display stock are refurbished display assemblies recovered from used systems which have been fully tested.
Some displays do come out of the factories in some form and often recovered from the waste bins before being destroyed. To combat this Apple stopped supplying the contractors the firmware for the camera unit, only at the time of fully assembling was the firmware installed. In the newest models the display is serialized which makes salvaged displays and even used ones not usable.