The whole "old installer" and "bootable disk" has been a pain-point since 10.8 for me. I have done 4 or 5 clean installs for friends in the last 6 months, and I tried to make a 10.10 or 10.11 bootable USB... no go - each time, a new issue.
I have ended up every time using my older 10.8 (ML) install USB every time, then just firing off the free App Store upgrade to 10.11.
I have ended up every time using my older 10.8 (ML) install USB every time, then just firing off the free App Store upgrade to 10.11.