If you have several galleries and want to use the shortcode to link to each specific gallery in a post, and you get the same gallery every time no matter what you post. For example, your shortcode = my-gallery and shortcode = another-gallery would bring up the same gallery.
It is possible that you are using wrong value in the shortcode. It is necessary to insert "post id" instead of "post slug" in the shortcode (ie. numbers, not letters).
To fix this go to the page of the single gallery editing page in your admin panel and there will be the path like "wp-admin/post.php?post=1784&action=edit" in the line of the browser, where 1784 is your "post_id".