I would like to argue against this, though what I say may not be widely accepted by religious or people of other beliefs. It is a definite fact that the human mind absorbs much of what the body experiences, most of it is subconscious and is not 'easily accessed'. In this sense, all this information, as random as it may be, is collected within the human mind. Now, when one coins the term 'Deep Trance Meditation' I would assume they would refer to a state of 'unconscious consciousness', meaning that they are able to move their physical body freely but their mind is completely vulnerable or in 'sleep' most would say. In simpler words, they're dazed.

While in this state of 'unconscious consciousness' another person, perhaps a scientist, could ask this person about mostly anything. Responding to the question, they will answer subconsciously with whatever info they may have absorbed over their life time. As I would like to say it "They're checking the bank for some cash."

If one would follow the pre-stated, it would point you in the direction that when someone remembers a 'past life' they are usually tapping into the knowledge which was dormant and cumulative. Please make a note that the this does not need to be triggered by more than one person. In fact, it could be triggered alone as you subconsciously pry around your 'memory bank' in a state of 'unconscious consciousness'.

Though, if one were refer to the reports and documentations... it would be an obvious fact that most, if not all, are flawed. Flawed in the way that they have not documented every second of the person's life. With this being said, they leave gaps of time in which the person may collect certain information, subconsciously or consciously. Or... one could say that it is a whole Conspiracy (not the best hypothesis, but it should not be excluded as a possibility).

Though, back to the topic of how many past lives on would be able to have... hypothetically, it would be infinite.