As I discuss in this answer, the Hare Krishna mantra, popularized by Chaitanya Mahaprabhu and his Gaudiya Vaishnava followers (especially the organization ISKCON), originates from the Kali Santarana Upanishad, which you can read here. The Kali Santarana Upanishad is widely considered by many to be a later interpolation, for multiple reasons: there are no ancient commentaries of it or ancient references to it; I think it's the only Upanishad that mentions the Yuga system, which was mainly revealed to human beings in the Itihasas and Puranas; it refers to the conversation happening at the end of the Dvapara Yuga, which would only make sense if the reader is presumed to be living long after the beginning of the Kali Yuga etc.
My question is, what is the earliest known mention or record of the Kali Santarana Upanishad? This book merely says that it dates to before the sixteenth century, presumably because the popularization of the Hare Krishna mantra dates to the sixteenth century. Now the Kali Santarana Upanishad is listed in the Muktika, the canon of 108 Upanishads, but the Muktika was passed down by oral tradition, and we only have written records of the Muktika from the seventeenth century onwards. So the Kali Santarana Upanishad could have been a late addition to it.
Are there any references to it dating back significantly before the sixteenth and seventeenth centuries?