I think yours is polished vs. brushed only because it is rose gold, not so much because of the manufacturing date (though Lange did start brushing more rose gold cases after 2015). Unless I'm mistaken (which is quite possible), this surface is still polished on the current RG 1815 model (235.032), whereas it is brushed on all the old and new 1815 variations in all other case metals (YG/WG/PT/HG).

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