2012... which means the flipper just bought recently (late 2012 or early 2013) and sold after a few months for >3X the retail price
Patek will definitely track down the flipper and AD and blacklist the flipper and may give a slap on the wrist for the AD
For all we know, the AD might have flipped it on its own
I have not heard any news from my sources in Hong Kong and China about 5131 being discontinued
But if the catalogue says so, perhaps Christie's know something that we do not