For words that have only 3 letters, there isn't a 4th letter. For example with the word “insert”, there isn't any much more letters Later on and thus must be the word "increase". The word “addict” is within the BIP39 wordlist but you would have applied “addi” for “addict”. Using https://thekiwisocial.com/story4244107/not-known-facts-about-bip39-english-words