For words that only have 3 letters, there is no 4th letter. For instance with the word “include”, there won't be any far more letters Later on and thus needs to be the word "incorporate". The word “addict” is during the BIP39 wordlist however, you would've employed “addi” for “addict”. https://socialmediainuk.com/story20291368/details-fiction-and-bip39