I don't see any issue there./dev/disk0 (internal, physical):
#: TYPE NAME SIZE IDENTIFIER
0: GUID_partition_scheme *480.1 GB disk0
1: EFI EFI 209.7 MB disk0s1
2: Apple_HFS Macintosh HD 478.3 GB disk0s2
3: Apple_Boot Recovery HD 650.0 MB disk0s3
I had no such problem as the one you report.To my understanding this is what I did; downloaded installer from AppStore, quit it, and went to Terminal to run the command as listed above (from within my booted 10.12.6 install).
I did; now it refuses to download installer information to target volume. Not sure what's going on. Will continue to investigate.I had no such problem as the one you report.
Maybe your download of the installer is corrupt.
Re-download from the Mac App Store.