For words that only have 3 letters, there isn't any 4th letter. For instance with the word “increase”, there aren't any additional letters Later on and therefore should be the word "include". The word “addict” is within the BIP39 wordlist however, you would've applied “addi” for “addict”. Mnemonic words illustrations https://thefairlist.com/story9057697/new-step-by-step-map-for-ledger-seed-phrase-bip39