For words that only have 3 letters, there isn't a 4th letter. One example is with the word “add”, there are no much more letters Later on and thus have to be the word "include". The word “addict” is in the BIP39 wordlist but you might have utilised “addi” for https://bookmarkingalpha.com/story18812897/bip39-seed-phrase-mnemonics-generator-an-overview