For words that have only 3 letters, there isn't a 4th letter. For instance with the word “incorporate”, there are no far more letters afterwards and therefore need to be the word "insert". The word “addict” is inside the BIP39 wordlist however , you might have made use of “addi” https://tornadosocial.com/story4360878/the-ultimate-guide-to-bip39-seed-phrase-mnemonics-generator