I have a right side wiper & connecting linkage that fits my '31 but haven't put it on the car.
Does anyone know if it's aftermarket? I have not
seen it listed anywhere by Chevrolet. Do all '31
wipers have Trico tag?

At the NW Meet in Bend Oregon, I saw a 31 Chev with a similar feature... it looked sort of cool, but obviously wasn't a genuine accessory. In fact, I suspect that they didn't come out until 3 or 4 years later, as double wipers became popular on later models...

I have 3 or 4 photos of it. A very clean installation with nearly identical wiper/spring arrangement. But, sorry, not a Chevy item.

Someone, please prove me wrong!

Well Billy, I'm going to prove you wrong.... but only partially wrong anyway, and that would be concerning when the right hand wiper came out. Yes, there was a right side windshield wiper assembly, and it was a genuine Chevrolet accessory. And, it didn't come out 3 or 4 years later like you said, but it came out in March of 1932! According to the Chevrolet literature, this right hand wiper accessory (it was called an "Auxiliary Wiper" in the parts book) was for the 1932 models only and it was not a retrofit for the 1931 models. There were no outside connections since everything was installed under the windshield header board. Also, the standard wiper motor had problems driving both wipers since it was only rated for one wiper, so a larger replacement wiper motor was also offered from Trico to drive the dual wiper set up. But, you are correct....a right hand wiper was not used in 1931 as a genuine Chevrolet accessory, but there were aftermarket right hand wiper units available as you stated. You have a keen eye!