I've just tried it and I was able to buy first wing of BRM and LoE after setting the date to 2016.
Karazhan was also in the list, but when entering it just shows a message and you can't start the prologue, so cannot buy it.
Naxx wasn't show, but as stated on a previous message just set the date to 2015 and it will.
The trick is that you hace to confirm the date change after the Heartstone title appears, not before.
I've just tried it and I was able to buy first wing of BRM and LoE after setting the date to 2016.
Karazhan was also in the list, but when entering it just shows a message and you can't start the prologue, so cannot buy it.
Naxx wasn't show, but as stated on a previous message just set the date to 2015 and it will.
The trick is that you hace to confirm the date change after the Heartstone title appears, not before.