For words that only have 3 letters, there isn't a 4th letter. For example with the word “insert”, there isn't any additional letters afterwards and thus has to be the word "increase". The word “addict” is in the BIP39 wordlist however , you might have made use of “addi” for https://mnobookmarks.com/story19398953/detailed-notes-on-copyright-wallet-seed-phrase-out-of-bip39