For words that only have 3 letters, there is not any 4th letter. By way of example with the word “incorporate”, there won't be any more letters Later on and thus needs to be the word "increase". The word “addict” is from the BIP39 wordlist but you would've applied “addi” https://bookmarkspy.com/story20907457/top-latest-five-bip39-seed-phrase-mnemonics-generator-urban-news