For words that have only 3 letters, there's no 4th letter. For instance with the word “increase”, there are no additional letters Later on and so have to be the word "include". The word “addict” is during the BIP39 wordlist but you might have made use of “addi” for “addict”. https://bookmarktune.com/story18861377/the-greatest-guide-to-seed-phrase-bip39