For words that have only three letters, there is no 4th letter. For instance with the word “include”, there won't be any more letters Later on and so should be the word "incorporate". The word “addict” is while in the BIP39 wordlist but you would have utilised “addi” for “addict”. https://directmysocial.com/story3618108/the-definitive-guide-to-bip39-seed-phrase