The resolution in conductivity between various clads, copper pennies, and silver dimes and quarters as well as large cents is rather close. There is a fine line between them in conductivity distinction, so that I never trusted what the machine thought it was on various detectors I owned that could make slight distinctions between them. Silver can and will read like "clads" or pennies due to dry conditions, being worn badly, on edge, masking, depth, or minerals. I've had sites where to the extreme a silver dime would ID as a much lower zinc ID than a copper penny. I've dug worn silver dimes that read like copper pennies. I've dug silver on edge or deep or masked by junk or minerals that read like clads, or even that sounded bad and I was sure was going to be a rusty old bottle cap on some machines.
When I'm old coin hunting, the only coin I really care about avoiding is zincs when there are billions at a site and I'm in the mood to avoid them, which read a good it further down in conductivity than most copper or bronze based pennies (not all, like fatty indians containing nickel which make then read even past zincs and into the tab range). Size of the silver coin can also cause it to read lower. A silver 3 cent piece reads as a zinc if memory serves without refreshing my memory looking at my ID chart. Half dimes probably at least as low as a wheat and probably down to the zinc range maybe.
When I'm after old coins, and the site has been pounded, and I'm in the mood to be picky- I'll only dig two types of coins....If they are deep, say 7" or more and thus perhaps beyond the reach of other machines in my mineralized soils, or beyond the reach of the particular coil they were using. Or, I will go after shallow coin hits too, but only if they are masked somewhat by trash to make me think they could perhaps be an old coin that others missed due to the masking. In those two cases (depth or masking), I will dig any "zinc" signal too.
The resolution is so fine on various high end of the scale coin types that it can make an ID floaty or jumpy, which can talk me out of digging a coin if I think it's trash by the ID instability. Yes, audio is king, but a VDI can convince you not to dig if you're tired or being particular that day, and that can cost you some nice coin finds. Primarily, besides going by the above deep or masked rules when after old coins at "dead" sites, if the audio hints to a sweet high silver tone I'll ignore whatever the VDI is trying to tell me and dig. Audio is by far the most reliable way to judge what is dig worthy, but just the same the VDI can offer valuable insight as well in certain situations, such as how false coin hits from iron tend to jump around randomly, where as a deep or masked coin might make a more steady less random climb in VDI to the coin range.
In a sense, there is an old saying that a bigger net catches more fish, so by way of having a larger "coin" ID that most coins fall under, at depth or in masking it may be easier to see what could be a coin, and not have the VDI trying to talk you out of it.
The only time I really care about splitting hairs on targets is with low and mid conductors, from foil up to tabs and with nickels in between. With a very high resolution in this low to mid range just below zinc pennies, I often find it useful to avoid a billion tabs at a site while doing after nickels or potential gold rings or buttons, and even after certain old odd coins that are supposed to read that low on the scale. Then I find it useful to split hairs and note VDI numbers of stuff. With such high conductivity resolution in this range, my nickel count has gone way up, since they ID distinctly below round and square tabs, and also well above most forms of foil or can shard trash. That's where I want to avoid a bunch of junk on particular days I'm being picky about things, and try to slant the odds in my favor by avoiding very common trash numbers present at a site.
There is also a gap, between the highest tab # and the lowest zinc penny #, where about a 3 digit VDI span is a "dead zone" of targets I rarely see, so I always dig those odd in between numbers when I come across them, hoping for a gold ring or some other good find, and often I have got some cool relics that way.
Summary on being able to tell silver from clads- Yes, with a good machine you can often tell a slighter "sweetness" or higher pitch to what should be silver, or say how fast the ID jumps up to "COIN" without as much wiggle work too, but just the same avoiding what you suspect is say a wheat while digging only silver is very risky. I often run across sites where it's obvious all the silver has been cherry picked, and will dig say 10 to 20 wheats in a few hours time with ease. I always smile when that happens, because I know very well they are passing some silvers that read just like a wheat or even lower for some odd reason. Not too mention any silvers dropped with those wheats that might be under them, because the detection field is only going to see the first metal object in the field unless they are at the same depth or such for the most part.
When a site is beyond dead, that's when I come back and work it from odd diagnal angles, and dig any iffy coin hit no matter how bad it nulls or sounds from other angles. Badly masked coins might not be seen unless hit from those quirky odd gridding angles human nature never does. People always grid parallel or 90 degrees to landmarks such as sidewalks, and even if they don't most people won't dig iffy coin hits, thinking they know better as to what is dig worthy. No machine, no matter how much technology crammed in the box, can make badly masked or mineralized conditions make all coins sound perfect. The trick is to lower your standards when a site is beyond "dead". If most will dig an iffy coin hit that is at least 75 or 80% "there", there lower your standards to say 30 to 40% "coin" and watch the finds pop out like magic...