For words that have only 3 letters, there is not any 4th letter. Such as with the word “include”, there won't be any additional letters afterwards and thus has to be the word "add". The word “addict” is during the BIP39 wordlist however, you would've employed “addi” for “addict”. A https://ticketsbookmarks.com/story18724607/bip39-seed-phrase-mnemonics-generator-an-overview