You can use something like SeatGuru before you book a flight to confirm the model. For instance, the LH490 flight on 4/9/2019 will be a 747-400: https://www.seatguru.com/findseatmap/findseatmap.php?airline...
Certainly there have been reports of pilots complaining that they didn't find out they'd be flying a MAX 8 until the last minute, and having to get "trained" on it during their ride to the airport.