I found it curious too when I saw Hearts of Stone discounted on the main page. I'm a proud owner of the main game, but I've been holding out on acquiring the season pass in case there's some kind of sudden discount window.
But thinking further, I feel it'd be pretty silly for them to charge a set sum for the season pass, then out of the blue offer a plan that allows buying both parts even cheaper pre-release.
Hearts of Stone currently has the full price of 9.99€, making it 8.49€ with the 15% discount.
I'm guessing here of course, but If Blood and Wine has double the content as Hearts of Stone, a logical pricing point for it would be 19.99€. With the same 15% pre-release discount, that will be 16.99€.
If both are acquired separately pre-release, the total will be 25,48€, making the season pass still slightly more affordable. Of course, you can shave another 1€ off, if you buy HoS now and then use the store credit acquired while buying B&W, meaning buying them separately would become about 50 cents cheaper.
I do think it's fair however that GoG does not take store credit into account, since this lovely site has hundreds of other things on which you can spend said change as well...
Post edited September 09, 2015 by drlaiho