For words that only have three letters, there is not any 4th letter. As an example with the word “include”, there are no more letters Later on and therefore has to be the word "increase". The word “addict” is from the BIP39 wordlist but you might have applied “addi” for https://health-lists.com/story19666451/the-fact-about-valid-bip39-seed-phrase-that-no-one-is-suggesting