Silly question from The Cattery . . .
I have read that repeated attempts to re-flash the HG612 with an "unlocked" firmware image fail. Those attempts to re-flash are being performed via the Broadcom firmware upload page? (And not the GUI firmware upload page?)
Short comment: The are two separate locations from which one can flash the firmware to a HG612 device and they require the firmware to be in different format, dependant upon the instigating location. All HG612 firmware images that have been created, firstly by Asbokid and latterly by Wolfy (Howlingwolf) must be used via the Broadcom boot-loader firmware update page.