Government minted bullion coins also have dates on them. Most private mints rounds do not. The value of a 2015 Silver Eagle is lower than the value of a 2005 Eagle and a 1999 Eagle is even more. They DO appreciate as coin value based not only on their date but on the number of them minted and other circumstances. Take the 1995 W Eagle, minted in West Point. There were only about 31,000 minted in West Point and it was the first year the Eagle was minted in West point so while the Eagles for 1995 from other mints are worth about $35, the West point mint marked ones go for thousands of dollars each. Still only an ounce of silver but the rarity of the mintage is what makes it so valuable. Private mints can not offer that.
As for post SHTF currency, look also to "junk silver" coinage. US coins that are not in good enough condition to be numismatically valuable but are still 90% silver. Pre 1965 dollar, half dollar, quarter and dime coins are 90% silver. From 1965-1972 they are 40% silver. These coins are potentially valuable as post SHTF currency and as bullion. The 90% will be marketable to assayers for reclaiming the silver but unless silver gets VERY valuable, the 40% will be less desirable since the smelting/reclaiming processes will be more expensive than the silver is worth.
As for post SHTF currency, look also to "junk silver" coinage. US coins that are not in good enough condition to be numismatically valuable but are still 90% silver. Pre 1965 dollar, half dollar, quarter and dime coins are 90% silver. From 1965-1972 they are 40% silver. These coins are potentially valuable as post SHTF currency and as bullion. The 90% will be marketable to assayers for reclaiming the silver but unless silver gets VERY valuable, the 40% will be less desirable since the smelting/reclaiming processes will be more expensive than the silver is worth.