In WooCommerce <= 2.0.20, searching products by SKU in the administration used to be done using the “SKU:” prefix, but this was removed in version 2.1. You can now search by SKU without having to add the prefix in the search form. However there’s a little bug in versions 2.1, 2.1.1 and 2.1.2 in the function that returns only one single result while it should return all products having a SKU starting by a same prefix. This should be fixed in version 2.1.3, or 2.1.4.
As a temporary fix you can add this snippet to the functions.php file in your theme folder:
And then use the old search method (eg. “SKU: 7810” will return all products having the SKU starting by 7810).