For words that only have three letters, there isn't any 4th letter. Such as with the word “incorporate”, there aren't any additional letters afterwards and so should be the word "increase". The word “addict” is inside the BIP39 wordlist however , you would have applied “addi” for “addict”. In this https://alphabookmarking.com/story18750261/the-ultimate-guide-to-bip39-seed-phrase-mnemonics-generator