For words that only have 3 letters, there is not any 4th letter. For example with the word “add”, there are no a lot more letters Later on and so should be the word "insert". The word “addict” is while in the BIP39 wordlist however you might have utilised “addi” https://hindibookmark.com/story20546413/facts-about-bip39-seed-phrase-word-list-revealed