For words that only have 3 letters, there is absolutely no 4th letter. Such as with the word “insert”, there aren't any more letters Later on and thus has to be the word "incorporate". The word “addict” is inside the BIP39 wordlist but you would've utilised “addi” for “addict”. Art https://mediajx.com/story21596236/considerations-to-know-about-bip39-word-list-pdf