For words that only have 3 letters, there is no 4th letter. By way of example with the word “incorporate”, there aren't any a lot more letters afterwards and thus must be the word "incorporate". The word “addict” is inside the BIP39 wordlist but you would have used “addi” for https://bookmarkprobe.com/story19287553/5-simple-techniques-for-bip39-word-list-pdf