They figured out there was a time loop, they didn’t figure out how many times they have looped.

Copied from Wikipedia:

Initially, crew members are unaware of the loop. However, Dr. Beverly Crusher (Gates McFadden) begins to hear noises before she goes to bed following the poker game. Having a sense of déjà vu during the poker game and being able to predict the cards Data will deal during a subsequent loop, Crusher takes a tricorder with her to her room, records the voices, and later analyzes them to discover they are the panicked commands and broadcasts of the crew. The senior staff work out that they are stuck in the loop; the voices they are hearing are those of themselves from the previous loop just prior to the destruction of the ship. They evaluate the voices to determine that the loop is restarted due to the collision of the two ships but do not know how to avoid that collision in the first place. Data suggests that his positronic brain can be used to send a short message to himself in the next loop which may help them to avoid the collision. When they arrive at the anomaly, and after the collision, Data sends the message.

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Ok I’ve seen so many references to this episode, I now would like to watch it. What series/ep is it?