Products that are showing in public category section are not visible in admin side under category.

Hi, Tomorrow i insert some products using sql into category named "sale", by mapping those products into product_category_mapping table.
Insert into product_category_mapping (categoryid, isfeatureproduct, displayorder,productid) select 29,0,0,id from product where oldprice>0

But, the problem is that the products that are shown in public store under sale category some products are not visible under sale category in the category section, 15 products are missing from admin side under that category. I think that is due to display order? I set the display order 0 for all products that's why it is causing problem. What should i do to handle this situation? Is this a nop bug? Why some products are missing in admin side under sale category?