For words that have only three letters, there is not any 4th letter. Such as with the word “increase”, there isn't any a lot more letters afterwards and so need to be the word "include". The word “addict” is in the BIP39 wordlist but you would've applied “addi” for “addict”. https://bookmarkeasier.com/story18845532/getting-my-bip39-words-to-numbers-to-work