You export your products and you get an error message like this one:

Product without reference (X-Y) ignored

This message indicates that the product doesn’t have a “Reference” field filled in, for example:

25-10-2014 08-22-13

The product reference is missing. Refer to how Validate your catalog structure.

You can then find a product displayed in this list of identifiers, thanks to its Product ID by searching in your catalog, for example:

25-10-2014 08-26-17