Google provides instructions for how to add a device to its two-step verification.
Add trusted computers and devices
Sign in on a computer or device you trust.
When you enter a verification code, select Don't ask again on this computer.
Unfortunately, these are inadequate. For example, on many devices I wish to add, I am already signed in. When I sign out and sign back in, there is no request for a verification code (so I can't select "Don't ask again on this computer"
Motivation
The reason for wanting to add more devices as trusted devices is because I recently updated my phone and Google's two-step verification will only allow me to carry out the second step of the verification on the old device. Thankfully, I hadn't yet wiped/sold it! Getting locked out of a Google account over something so poorly thought through would be disastrous.
Question
How do I add more devices as trusted devices for the purpose of two-step verification? (so that if one is not available, e.g. it's been sold, then I can do so on another device)