However, in running the extract-files, it's very often to see output like
remote object '/system/lib/egl/libplayback_adreno200.so' does not exist
It didn't say it's an "Error", but actually the script will just stop there, leaving the remaining blobs unextracted.
If you thought, oh, only one file does not exists, maybe not a big deal, so you continue to build the framework, it's highly likely that the framework you build will not work properly, due to lack of blobs.
Download a released Cyanogenmod for that device (the same version with the one you are trying to compiling), unzip it to a folder, suppose the folder is "/home/cm"
Then when running the extract-file.sh, instead of connecting your device to USB and extracting from device (which is the default behavior if you don't provide any argument to the extract-files.sh), you can simply run
(replace /home/cm to the folder where you unzip the Cyanogenmod, of course)
Then the extract-files.sh will copy blobs from that folder.
If there is still some file missing (e.g. libpn544_fw.so for Galaxy S3), then google it, download it and put it in the right path -- in general, missing blobs is not a good thing, we should avoid it as much as we can, and that's why I commented out the text below, which is a very bad solution.