More nerdy site analysis junk here:
Back when I was CRHing on a regular basis, I started to get a "feel" for how coins were circulating in my area. For example, when you go through a few hundred bucks of pennies (discounting boxes that are nearly full of shiny new shield pennies), patterns begin to emerge. I was finding 1-2 wheat pennies per $25 on average, and about 20% coppers. This is what got me started with analyzing sites and logging the results in a database in the first place. If I hit a site hard and the coppers range significantly above or below this, I know something about the last time that it was hit. Likewise, if I dig up 30 pennies and one is a wheatie, I might know something there too. If a wheatie pops up again or two or more appear, it's probably not an anomaly. This also tells me something about when silver may have been dropped there, and how far it's sunk. That's also why I don't get overly angry when beaver tails, or bottle caps and clads pop up at depth either. All of this tells me about how the site was used, and how it's been hunted since.
If there's little or nothing under a certain date (typically 1965 in my experience...go figure), it's safe to assume that someone has hit it hard since then. It's also safe to assume that they missed something, but don't expect silver hordes. In all likelihood, it's been hit multiple times since then with machines of different pedigrees, which would explain why the shallow coppers and silvers (and later the deeper silvers, when cherry-picking became easier) aren't in abundance.
Honestly, I'm more excited by the large amounts of clad; I could care less about the clad itself, but it's a useful tell. You just don't find that on public property around here. The prevalence of quarters and other high conductors tells me that either it hasn't been hit in a long time, or else the person who hit it was a superbly capable high grader with a good machine. The obvious silver coins are likely gone...but if they were high grading like that, they missed the gold. I'm more than happy to clean up after people who hunt like that.
I become alarmed when there's nothing but shallow clad or, worse, nothing at all - not even trash. That tells me that someone has been hitting it hard recently and is digging the pull tabs and nickels, meaning that they likely got the gold too. A site like that is a waste of time. But a site with decades of clads piled up on it? I'll certainly dig them, but you can bet the bank that I'll be digging up the mid conductors in the process. One piece of gold makes up for a lot of trash.
Again, don't worry about the dates on the clad coins because it really doesn't tell you anything. (Pennies are more informative due to the later transition and the fact that coppers still circulate commonly.) I dug up two more '65's last weekend and only one of them looked like it had been there for a while. '65's still circulate. A '65 could have been dropped yesterday. You could get one in your change tomorrow. They turn up all the time and they frustrate me all the time. The date on the coin merely establishes the early limit for when the coin was dropped, but has no bearing on when it happened. Corrosion will tell you more. Even depth will tell you more if you're recovering other objects that can be dated in the area at the same depth. That hard cutoff in target dates does suggest that someone cherry-picked the site at some point in the past.
By all means, keep looking for the silver, but don't get hung up on the clad dates.
