If you have access to ExpertFlyer as a paid subscriber, Baisc or Premium, or have received a limited Guest account you will see all the DL availability. There is no difference.

If you request to see G/Z/V/X inventory by specifically requesting it in the Class box on the Flight Availability query entry screen, DL will try to return the availability on the date and route you requested for that class either on DL metal or a codeshare whichever is available. If it only shows availability on codeshares, it means that there is no availability on DL metal for the route, date and time requested.