Richard P. Taylor looks at the evidence and comes to the following conclusion:
While a few Western sources by Blavatsky's time had made brief mention of the existence of a Kålachakra Tantra and the existence of a "Gyut" section of the Buddhist canon, Blavatsky gave significantly more information, which has turned out to be correct. (1) Tibetan tradition does in fact have a record of more extensive and explanatory Tantras, which do not exist in the Tibetan Canon. (2) The Kålachakra system is largely cosmological and deals with the creation of the universe from space, through six elements, with extremely complex numerology and astrology. This is the subject of the entire volume one of Blavatsky's Secret Doctrine. (3) The Kålachakra is associated with the scholarly tradition of the Paˆchen Lamas, who are in fact considered the tutors of the Dalai Lamas. None of this proves that there is in fact a secret M¨la Kålachakra Tantra, or that Blavatsky (or her teachers) had access to it. But it does suggest that Blavatsky knew what the Buddhist Tantras were, knew their content and philosophical import better than any Western contemporary, and knew bona fide Tibetan traditions surrounding them. This alone gives strong reasons not to dismiss her claims out of hand.
This is perhaps an overstatement of the facts. HPB has gone on record that her teachers are not Tibetan monks. Their writings show a lack of reference to the orthodox canon, as someone within the tradition would have known; neither is there the familiar deity yoga prevalent in Tibetan Buddhism. It is a philosophical interpretation of ideas found throughout the trans-Himalayan region, a tribute to the area’s syncretism, though tinged with certain concepts connected with esoteric Tibetan Buddhism, such as “yogi of ‘Time’s Circle,’” a phrase having a specific context. Could a woman with minimal education have cribbed together a system so coherent that it still attracts a worldwide following a century after her death? Possibly. But this would make her one of the most remarkable thinkers of our time, deserving of even more attention.