For words that only have three letters, there's no 4th letter. For example with the word “insert”, there are no far more letters afterwards and so have to be the word "include". The word “addict” is while in the BIP39 wordlist however you would have used “addi” for “addict”. In https://naturalbookmarks.com/story19002015/new-step-by-step-map-for-ledger-seed-phrase-bip39