For words that only have 3 letters, there is absolutely no 4th letter. Such as with the word “increase”, there are no extra letters Later on and therefore have to be the word "incorporate". The word “addict” is within the BIP39 wordlist however , you would have applied “addi” for http://edgargvkh682.theburnward.com/from-mnemonics-to-security-understanding-bip39-passphrases-and-their-importance-in-copyright