I installed GrapheneOS on a Pixel 7. I reverted back to the stock Google Android OS 13 using the process at this link: https://grapheneos.org/install/web#replacing-grapheneos-with-the-stock-os
The processs tells you to erase the custom Android Verified boot Key to untrust it:
"The GrapheneOS factory images flash a non-stock Android Verified Boot key which needs to be erased to fully revert back to a stock device state. Before flashing the stock factory images and before locking the bootloader, you should erase the custom Android Verified Boot key to untrust it"
I followed the process and clicked the "Remove non-stock key" button on the web page. There was no confirmation that this action erased the key properly. Nor was there any error message.
My question is how do I know that the non-stock keys were erased? How can I verify that the non-stock keys are really erased?