For words that only have three letters, there is not any 4th letter. As an example with the word “increase”, there isn't any additional letters afterwards and thus must be the word "add". The word “addict” is during the BIP39 wordlist but you would have made use of “addi” for https://fellowfavorite.com/story20212704/the-5-second-trick-for-ledger-seed-phrase-bip39