It is good to make it clear that DN1 is not only talking about Contemplatives and Brahmins from the time of the Buddha.
“In the first case, bhikkhus, some recluse or a brahmin, by means of ardour, endeavour, application, diligence, and right reflection, attains to such a degree of mental concentration that with his mind thus concentrated, [purified, clarified, unblemished, devoid of corruptions], he recollects his numerous past lives: that is, (he recollects) one birth, two, three, four, or five births; ten, twenty, thirty, forty, or fifty births; a hundred, a thousand, or a hundred thousand births; many hundreds of births, many thousands of births, many hundreds of thousands of births. (He recalls:) ‘Then I had such a name, belonged to such a clan, had such an appearance; such was my food, such my experience of pleasure and pain, such my span of life. Passing away thence, I re-arose there. There too I had such a name, belonged to such a clan, had such an appearance; such was my food, such my experience of pleasure and pain, such my span of life. Passing away thence, I re-arose here.’ Thus he recollects his numerous past lives in their modes and their details.
SuttaCentral
For example, there are Contemplatives and Brahmins who lived at the time of Buddha Kassapa.
and just as the Dhamma taught by Buddha Kassapa was not present when the Buddha of the present age was learning to meditate before his Enlightenment.
The Teachings of these Contemplatives and Brahmins mentioned in DN1 also did not exist at the time of the current Buddha.
“In the first case, bhikkhus, some recluse or a brahmin, by means of ardour, endeavour, application, diligence, and right reflection, attains to such a degree of mental concentration that with his mind thus concentrated, [purified, clarified, unblemished, devoid of corruptions], he recollects his numerous past lives: that is, (he recollects) one birth, two, three, four, or five births; ten, twenty, thirty, forty, or fifty births; a hundred, a thousand, or a hundred thousand births; many hundreds of births, many thousands of births, many hundreds of thousands of births. (He recalls:) ‘Then I had such a name, belonged to such a clan, had such an appearance; such was my food, such my experience of pleasure and pain, such my span of life. Passing away thence, I re-arose there. There too I had such a name, belonged to such a clan, had such an appearance; such was my food, such my experience of pleasure and pain, such my span of life. Passing away thence, I re-arose here.’ Thus he recollects his numerous past lives in their modes and their details.
SuttaCentral
“Herein, bhikkhus, a certain recluse or brahmin, by means of ardour, endeavour, application, diligence, and right reflection, attains to such a degree of mental concentration that with his mind thus concentrated he recollects his numerous past lives: that is, (he recollects his past lives throughout) one aeon of world-contraction and expansion, throughout two, three, four, five, or ten aeons of world-contraction and expansion. (He recalls:) ‘Then I had such a name, belonged to such a clan, had such an appearance; such was my food, such my experience of pleasure and pain, such my span of life. Passing away thence, I re-arose there. There too I had such a name, belonged to such a clan, had such an appearance; such was my food, such my experience of pleasure and pain, such my span of life. Passing away thence, I re-arose here.’ Thus he recollects his numerous past lives in their modes and their details.
SuttaCentral
In addition to the Contemplatives and Brahmins mentioned in DN1, they are from other times.
They can also be from other Cosmic Cycles … (other universes ?!)
The DN1 Brahmajālasutta, The Prime Net, it is a very vast Sutta that encompasses all of Existence, all of Samsara.
So we have to be careful to mention DN1 as an example that the Buddha learned to meditate with the Contemplatives and Brahmins mentioned in this Sutta.