For words that only have three letters, there's no 4th letter. For instance with the word “increase”, there aren't any more letters afterwards and so should be the word "include". The word “addict” is during the BIP39 wordlist however you would've employed “addi” for “addict”. The usage of BIP44 with https://doctorbookmark.com/story18870783/bip39-seed-phrase-fundamentals-explained