For words that have only three letters, there isn't a 4th letter. As an example with the word “include”, there aren't any extra letters Later on and so has to be the word "include". The word “addict” is while in the BIP39 wordlist however , you might have employed “addi” https://mysocialguides.com/story4439545/the-greatest-guide-to-seed-phrase-bip39