Ishvarakrishna's own verses refer back to earlier Samkhya teaching he did not originate, attributed by tradition to a teacher named Kapila and transmitted through a compiler named Pancasikha, but none of that earlier material survives as an independent text today. That makes the Samkhya Karika the earliest complete Samkhya work to come down intact, effectively the foundation the entire later tradition of commentary was built on rather than one voice among several equally preserved ones.
Later commentators, most influentially Gaudapada and, centuries afterward, Vacaspati Misra, wrote extended explanations that fixed the standard classical interpretation of the Karika's compressed verses, since the text's brevity leaves real interpretive gaps a commentary is needed to fill. Samkhya's dualist metaphysics also shaped the philosophy of Yoga directly: classical Yoga, as systematized in the Yoga Sutras attributed to Patanjali, adopts the Samkhya framework of purusha and prakriti nearly whole, differing chiefly by adding a personal god, Ishvara, as an aid to practice, a figure classical Samkhya itself, true to its own logic, does not require.
Modern scholarship on Indian philosophy, including Gerald James Larson's study of the school's history, treats the Karika as the essential primary source for reconstructing classical Samkhya on its own terms, independent of how later Yoga and Vedanta writers subsequently absorbed or argued against its dualist framework.