For words that only have three letters, there isn't a 4th letter. One example is with the word “add”, there are no far more letters afterwards and thus must be the word "increase". The word “addict” is from the BIP39 wordlist however, you would have used “addi” for “addict”. Using https://bbsocialclub.com/story20921679/an-unbiased-view-of-bip39-seed-phrase-github