1981 tach cluster with trip odo

[c10sport]

I pulled a tach cluster from a 1981 C30 yesterday at a local LKQ U-Pull-It and later I noticed it has a trip odometer. I pay close attention to tach clusters (I seem to have a fetish for them, this is my third 1980+ tach and my second found in a self serve yard in less than 6 months.) but this is the first one I've ever seen that's original - the truck had the correct tach cluster RPO on the SPID label - that had the trip odo. I watch them on ebay all the time and again, I've never seen one with a trip odo.

What years were the trip odo available? (besides 1990-91 with the electric speedo)

Truck had delay wipers, tach and little else. I also grabbed the working delay wiper pieces for my truck.