Not all hoards on the market are recent finds. For a case in point, see this press release about the upcoming sale of the Bishop's Wood Hoard of 1895. See http://news.coinupdate.com/the-bishops-wood-hoard-of-roman-coins-0145/
Other times, groups of coins from older hoards also come up for sale. A few years back coins from the "Paeonian Hoard" sold by Sotheby's in 1969 came onto the market. I understand a coin dealer who had bought a large group of the coins back in 1969 decided to disburse some coins he had saved as he neared retirement.