For words that have only three letters, there isn't any 4th letter. For example with the word “increase”, there aren't any more letters Later on and thus need to be the word "include". The word “addict” is from the BIP39 wordlist but you might have used “addi” for “addict”. This https://dirstop.com/story21855545/the-greatest-guide-to-seed-phrase-bip39