For words that have only three letters, there is no 4th letter. As an example with the word “insert”, there aren't any more letters Later on and thus must be the word "insert". The word “addict” is from the BIP39 wordlist but you might have utilised “addi” for “addict”. Artwork https://bookmark-nation.com/story18676368/an-unbiased-view-of-bip39-seed-phrase-github