Possible selection in set expression

[#1]

I am using a set expression =

(Sum({1<Product=p(Product), Year={2014}>} Volume)) - Sum({1<Product=p(Product), Year={2013}>} Volume)

But the problem with this expression is when i select Year 2013 the product gets filtered and possible products are of Year 2013 and the first part of the expression also takes Year 2013 products. I want

Sum({1<Product=p(Product), Year={2014}>} Volume)) Sum({1<Product=p(Product), Year={2013}>} Volume) to take 2013 products even if i have selected any year.

Is this possible

Thanks and Regards,

Sumit