For words that only have 3 letters, there is no 4th letter. For instance with the word “incorporate”, there won't be any far more letters afterwards and thus should be the word "increase". The word “addict” is in the BIP39 wordlist however , you would've utilized “addi” for “addict”. A https://pageoftoday.com/story4238232/the-ultimate-guide-to-bip39-seed-phrase-github