For words that have only three letters, there is no 4th letter. For example with the word “include”, there are no additional letters afterwards and so must be the word "increase". The word “addict” is from the BIP39 wordlist but you would have made use of “addi” for “addict”. In https://sociallawy.com/story9080335/the-2-minute-rule-for-bip39-all-words