For words that have only 3 letters, there is not any 4th letter. As an example with the word “add”, there isn't any much more letters Later on and thus have to be the word "insert". The word “addict” is in the BIP39 wordlist but you might have utilized “addi” https://socialistener.com/story5099727/the-ultimate-guide-to-bip39-seed-phrase-github