For words that only have 3 letters, there is not any 4th letter. One example is with the word “include”, there won't be any far more letters afterwards and therefore needs to be the word "add". The word “addict” is from the BIP39 wordlist however you would've used “addi” for https://mnobookmarks.com/story18858800/the-ultimate-guide-to-bip39-seed-phrase-mnemonics-generator