Newly Minted: unlimited

Unlimited mode is an Earlier or Later run. You are shown one known word with its real take-off year and one hidden word, and you call whether the hidden word took off in books earlier or later than the known one. The two words are always at least 5 years apart. A right call swaps the hidden word into the known slot and keeps your run going; a wrong call reveals the answer and ends it, and Play again starts a fresh run. Unlimited mode skips words scheduled for recent and upcoming daily puzzles, so practicing never spoils a daily answer.