The 'sutra' period during ancient education was assumed to be equal to

The 'sutra' period of ancient learning was taken to fall alongside the Upanishadic period.

The Vedic period, being the earliest Samhita layer, is far older than the sutra phase.

The Bhakti period belongs to a much later devotional age and not to Vedic times.

The Poorva Mimansa is a school of philosophy, not a chronological period.

In this scheme the terse sutra texts are grouped with the reflective Upanishadic stage.

Sutras are compact aphorisms meant to compress large teachings into few words.