And if the planet was surveyed and nothing was found... can it be groundsurveyed and find anything? because it does not show any number.
If there is no potential (number) then there is no reason to send ground teams, they will find nothing. According to Steve, there is about 1 or 2 bodies with potential per system. Some more info from Steve:
The chances that an eligible body (4000 km diameter) will have ground survey potential is equal to:
None 60%, Minimal 20%, Low 10%, Good 6%, High 3%, Excellent 1%.
I dont think that it is possible to have body with no minerals generated to have potential for ground survey.