Umm, that seems like a random date range. It isn't. This is the date range some people found out that the Onslaught fetch lands were going to be in Modern Horizons 2, and this is the date range when all those people went on a buying spree for the Onslaught versions of the cards.
Polluted Delta
Blood-Stained Mire
Ummm, what a coincidence... Well, except it sure does not look like a coincidence that all of these cards doubled in price within the same week and more than a month before we the peasants found out.
