For words that only have 3 letters, there isn't any 4th letter. For example with the word “increase”, there won't be any far more letters afterwards and so has to be the word "add". The word “addict” is from the BIP39 wordlist but you might have used “addi” for “addict”. https://bookmarklayer.com/story18826157/little-known-facts-about-bip39-seed-phrase-list