At least on the SoC level the silicon for the next two chips has been more or less finalized with the next one most likely being already taped out for sampling.

At least on the SoC level the silicon for the next two chips has been more or less finalized with the next one most likely being already taped out for sampling. Everything thing that Apple outsources has also likely already been finalized for the next model at the least especially the screen. Other components that are closely tied to the SoC like the memory have been selected and contractually procured. One year before launch PCBs are should already being finalized, fully assembled phones with some features missing like maybe the next years cameras also probably exist in labs. Apple launches phones relatively very shortly after their announcement and these phones need to be certified around the globe by various agencies a process that can take months and probably around half a year if not longer, other certifications like their IP rating also need to be completed well in advance. So overall on a yearly cycle the next model is pretty much already ready to go, and the one after that is quite close to being finalized too.