For words that only have 3 letters, there isn't a 4th letter. As an example with the word “include”, there are no more letters afterwards and thus should be the word "insert". The word “addict” is in the BIP39 wordlist however you might have employed “addi” for “addict”. A seed https://rotatesites.com/story20851357/an-unbiased-view-of-bip39-seed-phrase-github