For words that only have 3 letters, there is not any 4th letter. By way of example with the word “include”, there isn't any far more letters afterwards and therefore must be the word "insert". The word “addict” is inside the BIP39 wordlist however , you would have applied “addi” https://friendlybookmark.com/story18732090/ledger-seed-phrase-bip39-no-further-a-mystery