For words that have only 3 letters, there's no 4th letter. For example with the word “incorporate”, there aren't any a lot more letters Later on and so needs to be the word "add". The word “addict” is in the BIP39 wordlist but you might have utilised “addi” for “addict”. https://admiralbookmarks.com/story19052550/little-known-facts-about-bip39-seed-phrase-list