For words that have only 3 letters, there isn't any 4th letter. For example with the word “insert”, there aren't any more letters Later on and thus have to be the word "add". The word “addict” is from the BIP39 wordlist but you would've utilized “addi” for “addict”. By adhering https://social-medialink.com/story4025914/bip39-seed-phrase-mnemonics-generator-an-overview