The words rta, rtambhara and prajna are defined as follows:
rta ————————- Unalloyed truth;
rtambhara ————- Full of rta;
prajna——————- Deep Understanding. Insight derived from meditation.
Yoga Philosophyof Patanjali by Swami Hariharananda translated by P. N. Mukherji
The term rtambhara prajna represents the deep understanding and insight that is derived by an Yogi through the power of his meditation from unalloyed truth or divine source. I will now post a passage that will better explain Rtambhara Prajna.
When the instruments of cognition are purified, the knowledge that
appears in the engrossed mind is called Rtambhara (lit. full of
unalloyed truth) justifying the name given to it. It retains and
sustains truth alone with no trace of misconception. It has been said
in this connection:"By study of religious books, by inference and by
attachment to the practice of mdeitation, developing intense insight
in these three ways, perfect Yoga (or seedless, i.e., objectless
concentration) is acquired (1)."
(1) *The Sruti, i.e. the Upanishads also say that realisation comes
through listening, contemplating and concentrating. If one learns by
listening only that Atman (the Self) is different from Buddhi (pure
I-sense), or that principles are such and such or that this sort of
state is Moksa (cessation of sorrow), he really does not get to know
much. Similarly, if by inference only one comes to know about Purusa
and other principles, there is thereby no chance of bringing about
cessation of sorrow. But when one constantly thinks of, or meditates
on such matters as 'I am not the body,' 'External things are sorrowful
and therefore should be forsaken,' 'I shall not resolve on worldly
affairs,' etc., and fully realises their essence, then one is on the
right roda to liberation. If, however, one comes to learn by reasoning
only that he is not the body and yet is affected by its distress or
pleasure, there is hardly any difference between him and an ignorant
man.
There cannot be any better knowledge of an object than what can be
acquired by Nirvichara Samadhi. That is why it is complete truth.*
Yoga Philosophyof Patanjali by Swami Hariharananda translated by P. N. Mukherji
It is difficult to give any evidence if such a state was reached by an enlightened soul.