For words that only have three letters, there's no 4th letter. Such as with the word “increase”, there are no more letters afterwards and therefore have to be the word "add". The word “addict” is within the BIP39 wordlist however you would have employed “addi” for “addict”. To test to https://bookmarksden.com/story18961477/getting-my-bip39-words-to-numbers-to-work