Is the back of Omega 424. 13.40.20.03.002 hollow?

It is not hollow. There are few back-wearing models in Omega Disc Flying Series. But now the new models of the 8500 movement are all worn on the back. Omega is a famous Swiss brand, founded in 1848, and is famous for its wristwatches. Omega has four classic wristwatch series, namely Constellation Series, Motorized Altman Series, Disc Flying Series and Hippocampus Series.