For words that only have 3 letters, there is not any 4th letter. By way of example with the word “include”, there are no far more letters afterwards and therefore must be the word "increase". The word “addict” is while in the BIP39 wordlist but you would have applied “addi” https://livebackpage.com/story4365097/an-unbiased-view-of-bip39-seed-phrase-github