For words that only have 3 letters, there's no 4th letter. As an example with the word “incorporate”, there aren't any much more letters Later on and so needs to be the word "insert". The word “addict” is while in the BIP39 wordlist however , you might have employed “addi” https://bookmarkjourney.com/story19050175/an-unbiased-view-of-bip39-seed-phrase-github