For words that have only 3 letters, there is not any 4th letter. For example with the word “increase”, there aren't any more letters Later on and so need to be the word "incorporate". The word “addict” is within the BIP39 wordlist however, you would've applied “addi” for “addict”. To https://maximusbookmarks.com/story18966547/phrases-with-bit-an-overview