that 1803's were rohdium coated for an extra brilliant shine.
I also use two ex-Rolex watchmakers here in Bangkok who say they were coated for sure. Also if you take a yellowed WG for a Rolex service they will offer to re-plate.
I have also seen WG bracelets (not mine) brushed back before recoating and were yellowish, but more recently >>>
I bought one that has never been serviced: Centre watch.
Take a look at the scans of the centre watch where the rhodium is wearing off and compare the colour to the two outer watches that do have multiple service marks and make your own opinion.