There have been instances where the Federation itself has apparently "forgotten" about the Prime Directive. One such was when Captain Kirk was ordered to open negotiations with the Capellans for a valuable ore, despite the culture being a pre-warp civilization. (TOS: "Friday's Child"). Another was when Kirk was ordered to organize the defense of the planet Organia, despite the appearance that the inhabitants were a pre-warp civilization. It could be argued, however, that with the impending Klingon invasion of the planet, that the Directive was rendered moot at that point. (TOS: "Errand of Mercy")
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Restricting contact to civilizations which had developed warp drive was never a condition of the PD during ST. That is strictly a TNG invention.