For words that only have 3 letters, there isn't any 4th letter. For example with the word “add”, there won't be any much more letters Later on and thus need to be the word "include". The word “addict” is within the BIP39 wordlist however , you might have made use https://franciscougju442.bravesites.com/entries/general/Opening-the-Power-of-BIP39-An-Extensive-Consider-Word-Lists-and-Secure-Budgets