Kibbush Yachid

The gemara talks about an area called Surya which, during the times of kedusha rishona, was captured "by individuals" and not by the whole Klal Yisroel (what exactly this means is the subject of another discussion). There are various halachos of Eretz Yisroel which, even nowadays, Surya is different than "bona fide" Israel.

This is somewhat problematic because wasn't the kedusha rishona batel? If that is the case, then if Surya was part of kedusha shniyah it should be the same as the rest of Israel. And if not, it should be total chutz la'aretz. Why should Surya be any different nowadays?

Rav Chaim in Stencils (on the din of Yesh Kinyan L'Akum) explains that kedusha shniya must literally be "the second". It has to be built off kedusha rishona. Thus, Surya remains different even in kedusha shniya because its kedusha shniya is built off of a kibbush yachid. This is another example of kedusha rishona still being in effect for some dinim (see this post for other examples).