For words that only have three letters, there isn't a 4th letter. Such as with the word “insert”, there isn't any extra letters Later on and thus should be the word "increase". The word “addict” is inside the BIP39 wordlist but you would've applied “addi” for “addict”. BIP39 and 44, https://rotatesites.com/story20085017/the-5-second-trick-for-ledger-seed-phrase-bip39