SMD LED polarity marking: is the cathode marking standardized?
It is entirely per component manufacturer, and when the PCB is manufactured some companies will ask that component placement overlays are given with designators are provided and polarity marks for all polarized components are shown. 

It's also a good idea to make a couple of test boards and hand solder and get familiar with the components to identify this kind of issue prior to sending in large batches to get assembled. 

I've made my own altium footprints with silkscreen diode style symbol showing polarity, which sits in between the pads. It helps me with hand soldering too, and then it doesn't matter which product I get, which may have different markings. I guess there are tricky components though that even trick the manufacturer, if they do not check the mechanical data/datasheet of the component when putting it into the pick and place machines. 

Good luck getting it fixed hehe, will take someone a long time.