Your install.wim is larger than wimlib lzx:50, which is the default, but smaller than lzx:20. So probably it was compressed with DISM.Under normal circumstances, the two files should be the same size. Because install.wim is through lzx:20 rebuild.
Note that even if you used wimlib-imagex to update or export the file, it may still contain DISM-compressed data. (Some wimlib-imagex commands accept a --recompress option to force recompression.)
I don't know what is going here, but one possibility is that Windows Setup only looks in the first WIM part for the license file. I tried those split commands myself, and I noticed that in the install_ESD.wim case some of the files in '/Windows/System32/Licenses' end up in the second WIM part instead of the first as they do in the install.wim case. If that's the case, then it only worked on install.wim by chance, and the problem is really that Windows Setup (at least in Windows 8) doesn't properly support split WIMs.After testing, I found that the image split from install_ESD.wim will have an error of "cannot find the license terms". The install.wim split does not have this problem. Is there some problem with wimlib WIM<->ESD?