For words that have only 3 letters, there is no 4th letter. One example is with the word “include”, there won't be any more letters afterwards and so has to be the word "add". The word “addict” is within the BIP39 wordlist but you would've made use of “addi” for https://ok-social.com/story5115683/how-much-you-need-to-expect-you-ll-pay-for-a-good-bip39-seed-phrase-mnemonics-generator