For words that only have 3 letters, there is no 4th letter. As an example with the word “insert”, there won't be any additional letters Later on and therefore need to be the word "insert". The word “addict” is in the BIP39 wordlist however you might have utilised “addi” for https://getsocialsource.com/story4356352/bip39-seed-phrase-fundamentals-explained