For words that only have three letters, there is no 4th letter. For example with the word “add”, there are no a lot more letters Later on and therefore should be the word "include". The word “addict” is in the BIP39 wordlist however, you would have made use of “addi” https://mysocialport.com/story4392175/little-known-facts-about-bip39-seed-phrase-list