Different airlines have different requirements on how to compartmentalize the aircraft - small or large business class, first class or no first class, where to place toilets, storages and galleys ...
Since it's a serial production of aircrafts, outer body panels will be identical for all aircrafts of that type - the only difference is that they block off window positions by inserting an aluminium "sheet" in stead of the glass/plastic windows in the cut outs.
Most airlines will paint this "windows" in the body colour, but Lauda select to create an illusion of an unbroken line of windows for design purposes. Even where no cut outs are done, like this picture of the B737-6Z9 shows
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Photo © Viktor László - Budapest Aviation Photography
Look out for the "window" under the L in Lauda - it don't exist any window at that position on any 737NG, the space is allocated for the air-ducts to and from the AC-pack.