For words that only have 3 letters, there isn't a 4th letter. Such as with the word “increase”, there isn't any extra letters afterwards and so have to be the word "include". The word “addict” is in the BIP39 wordlist however , you would have applied “addi” for “addict”. In https://minibookmarks.com/story18809215/helping-the-others-realize-the-advantages-of-bip39-mnemonic-phrase-tool