For words that only have three letters, there isn't any 4th letter. Such as with the word “increase”, there are no a lot more letters afterwards and therefore needs to be the word "insert". The word “addict” is during the BIP39 wordlist but you would have utilized “addi” for “addict”. https://cyberbookmarking.com/story18745215/facts-about-bip39-seed-phrase-github-revealed