Technically, such coins - same as the 10 DM German coins - were "in circulation" back then. They were official currency, like any other Schilling coin or note. But of course thats not what people got them for. The goal was for most, to have all the coins that were issued over the years - and thats quite lot. Since the number of coins ws pretty small for each issue, it was kind a tricky to get your hands on them (at a bank) quick enough. Best was if you knew someone who worked there and would put one on the side for you.
Also technically, Schilling and DM, and all the other currencies in EU countries before the Euro was introduced, are still valid. You cannot use them to buy stuff in shops anymore, but you can send them in to the central bank of the country in question. They will then pay out the amount in Euro according to the official exchange rate that was set in 1999. Its thought that there are still billions of old money hidden in books and old furniture, which were forgotten to get exchanged at the time.
Ha, that I didn't know. Still not worth it I guess because the silver is worth more. People accumulating back then surely made a nice buck!
No, the coins are a better deal now. But if people find some money stash they can get it changed into Euro still, even after 20 years now.