Also, does anyone know if blockchain.info used 12 words pre 2016 upgrade?
AFAIK it had a non-BIP39 mnemonic phrase which is a backup of your login details, not a seed mnemonic.
Is it possible to generate addresses from the v2 xpriv? Or how was that done?
Technically, it's possible. But I have no "
v2 blockchain.info wallet" to test this.
You can experiment using iancoleman's BIP39 tool but instead of pasting a BIP39 seed,
paste the xprv to "
BIP39 Root Key", select "
BIP32" Tab and select "
blockchain.info" in the 'Client' drop-down menu.
For your safety, launch BIP39 tool offline from source.