The Prime Directive wasn't mentioned until the end of the first season, and it wasn't defined until the end of the second season. And, provided someone previou

The Prime Directive wasn't mentioned until the end of the first season, and it wasn't defined until the end of the second season. And, provided someone previously broke the Prime Directive, inadvertently or not, Starfleet personnel are permitted to directly intervene and ignore the Prime Directive to minimize the harm caused. And most cases where Kirk "violates" the Prime Directive, someone else already interfered, meaning no violation occurred.