After extensive testing with every Gen. 5A drive we could get our hands on, it appears that 128GB SSDs with part numbers beginning with 656-0074 and 256GB SSDs with part numbers beginning with 656-0076 are only compatible with the model A1708 laptops from the Mid 2017 release. Only the schematics for 820-00875 is available, in this one U8640/R8645 are populated while R8641/R8642 are not. As per article 3.a, please link to the original article at https://blog.piernov.org/a1708-ssd/ .