I'm pretty sure that it doesn't have anything to do with the grill cloth, but then again. I know that to get these with the RR finish they had to be special ordered from the factory also the cost was considerably more than in one of the other finishes. Since 79 was the only year they would have been available I can't imagine the production numbers being very high. Thanks for your time by the way, I do appreciate it. Oh and if by chance you might know someone that's in the market to buy a small to medium size lot of vintage electronics I've got one for sale. I'll be 70 this year been doing this since the early 70s when I was in the service, my wife says it's time to let it go. There are some very nice pieces in this collection, including tube amps many tubes test equipment reel to reel pre amps power amps many speakers turntables receivers anyway enough to fill a medium size U-Haul truck, thanks for letting me ramble.