GPLv2 does not require you to make your source changes public, it only demands that this remains an option for anybody who acquires a license from you. So if I

GPLv2 does not require you to make your source changes public, it only demands that this remains an option for anybody who acquires a license from you. So if I sell you software under the GPL, I have to provide you the source. You are then allowed, but not required, to publish the source.