Scholarly opinion is as follows:
https://ipfs.io/ipfs/QmXoypizjW3WknFiJnKLwHCnL72vedxjQkDDP1mXWo6uco/wiki/Mudgala_Upanishad.html
The author or composition date of Mudgala Upanishad is unknown. Jan Gonda – a professor of Sanskrit and Dutch Indologist, states it is a late Upanishad.[4] The style and structure of Sanskrit words used by the text suggest it to be a medieval text.[7][8] The text, states Klaus Witz, is a post-Vedic but early Vaishnava Upanishad.[9] The Upanishad reflects an integration and a harmony of Vedic doctrines with those of Vaishnava doctrines.[10]
https://en.wikipedia.org/wiki/Subala_Upanishad
The Subala Upanishad, together with the relatively older Mudgala Upanishad, are two Upanishads that discuss the Purusha Sukta of Rigveda,[5] both notable for asserting that Narayana (Vishnu) is the Brahman (Highest Reality, Supreme Being).[5][6][7] The Subala Upanishad text differs from Mudgala Upanishad in presenting more verses of the Purusha Sukta,[5][8] being longer, and for declaring Narayana to be the father, the mother, the refuge, the friend and the goal of every living being.[4][6]
The author or composition date of Subala Upanishad is unknown. Hans Hock states that it is a late Upanishadic text.[12]
Is this the consensus as to the dates of these texts?
