Its admittedly a poorly lit image of the stamp, but I also think it may be a '70s cymbal. I don't think its '60s since the 3 dots seem to be missing.
I don't see it that way myself. I see enough 60s stamp diagnostics, including the 3 dots.
I also see factory rivet flaring vs post factory rivet flaring, although that isn't 100% diagnostic. All we can say is that the flaring pattern is consistent with factory. Some drum shops may have purchased whatever the special tool the Zildjian factory used to get the flare pattern. The other thing to check is that the holes are evenly spaced and exactly 1" in from the edge.
As far as price goes here are my published prices for the 20" size:
http://black.net.nz/avedis/avedis-prices.html#20
As you can see it doesn't really matter to price whether it is judged a 60s or a 70s produced cymbal. Same for the 22" size if you scroll up on that link. Based on 17 sales of 21" cymbals from the 60s and 70s, the expected median price is $150, which sits as expected between the 20" and 22" prices. Not that you buy cymbals by the inch.
I haven't done any specific analysis to look at the effect of removing rivets on the expected price. I've recorded thousands of cymbal sales to get reliable statistics, but in order to simplify my data entry task I haven't kept detailed records of the rivet status of each cymbal (eg 8 holes but only 4 rivets in place). That's a bit too nerdy even for me. I do note other aspects of condition, but that's usually not about rivet detail. Prices are variable enough that it takes good sized representative samples to get reliable estimates. Obscure details like number of missing rivets and an effect on price are not going to be easy to pick up given all the other variation in play.
As to the question of it looking exactly like a Rock Ride: 21" cymbals have been around since at least the Trans Stamp era, and they are common enough from the 1960s. Rock Rides came in at 1973 so I wouldn't expect to find many with a 1960s trademark -- although who knows for sure. There is a difference in bell size (diameter and height) between the 21" Rock Ride and the 21" Medium Ride. Bigger on the Rock. Scaling the bell on this one from the image (not super accurate) it looks like a 5" Medium Ride bell not a larger 6" Rock Ride bell. And on that note, Longjohn it would be great to get an accurate measurement of the bell on your 21" 70s Rock Ride. I've got one 6" measurement but a second confirmation would be great.
Yes it would be useful to know the weight, although that's not definitive either. I've got 48 weights recorded in my database for 21" A Zildjian cymbals from the Trans Stamp era to present, but I haven't done a proper analysis. Where they have model ink I can get specific models, but yes most older ones have the model ink missing. The Trans Stamps (and the recently launched A Avedis series) are light: 2072g - 2338g. Then there are plenty of 50s and 60s ones in the range 2350g - 2540g (including modern Sweet Rides). 60s and 70s come in at 2600g - 2850g, and then there are those Rock Rides 2900g - 3350g. These are just preliminary results subject to refinement when I get to it.
