For words that have only three letters, there is no 4th letter. Such as with the word “add”, there are no more letters Later on and so have to be the word "incorporate". The word “addict” is within the BIP39 wordlist but you would have applied “addi” for “addict”. You https://dailybookmarkhit.com/story19537739/bip39-phrase-generator-can-be-fun-for-anyone