For words that only have 3 letters, there is not any 4th letter. As an example with the word “increase”, there isn't any a lot more letters afterwards and so need to be the word "insert". The word “addict” is from the BIP39 wordlist but you would've utilised “addi” for https://wisesocialsmedia.com/story4568796/5-essential-elements-for-bip39-explained