For words that only have 3 letters, there is no 4th letter. One example is with the word “include”, there isn't any far more letters afterwards and so has to be the word "add". The word “addict” is from the BIP39 wordlist however , you would have applied “addi” for https://linkingbookmark.com/story18847549/how-much-you-need-to-expect-you-ll-pay-for-a-good-bip39-definition