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Your seed and passphrase is needed to generate your private keys for all of your Accounts, the pin is only needed to unlock the device itself, like on a mobile phone.
Public key is just the Account address and the private keys are needed to authorise a transaction.
The correct private key is generated (on your trezor) when you input the correctly passphrase.
Correct private key is seed 12/24words + (if enabled) correct passphrase, pin isn’t needed.