For words that only have three letters, there isn't a 4th letter. For example with the word “add”, there isn't any far more letters Later on and thus needs to be the word "incorporate". The word “addict” is within the BIP39 wordlist however, you might have applied “addi” for “addict”. https://bookmarkssocial.com/story18758979/how-much-you-need-to-expect-you-ll-pay-for-a-good-bip39-definition