How has this been verified? Is there a dissected HD-20 ROM dump somewhere? Or is it referenced in some Apple literature?
I ask because the original HD-20 startup disk (System 2.1/Finder 5.0) does contain the HD-20 icon in the System Folder SICN file. However, it's not in System 3.0 which has no SICN file at all. I feel like someone mentioned that the HD-20 ROM is coded like the 128/512K ROMs, making looking around it with Res-edit impossible. In which case, could the icon also be in the patched code file that the HD-20 INIT loads, or in lieu of residing on the HD-20 ROM itself?