Yes, Krishna was known, many ancient devotees have meditated on Krishna.
We get story of Ambarisha who used to meditate on Krishna's lotus feet.
This is also an ancient incident, Ambarisha was great-gradson of Vaivasvata Manu and Aṅgirā Ṛṣi and of Rathītara were known by the names of his descendants. the incident is very ancient one. 9th Canto describes the lineages of various kings in chronological order. Krishna is described at end of 9th Canto.
SB 9.4.18-20: He was sure to fix his mind upon the lotus feet of
Kṛṣṇa, to use his words to describe the qualities of [the Lord of]
Vaikunṭha, to use his hands for matters as cleaning the Lord's temple
and to engage his ears in listening to the transcendental talks about
the Infallible One. He used his eyes to look at the deities, the
temples and buildings of Mukunda, he used his body to be in touch with
the bodies of the devotees, he used his nose to smell the fragrance of
the tulsī leaves on the lotus flower formed by His feet and used his
tongue to relish the food that is offered to Him. By using his legs to
walk to the Lord's holy places, by using his head to bow down to the
feet of Hṛṣīkeśa and by engaging his senses more in being a servant of
Him than a servant of his lusty desires, he was alike the ones who
seek their refuge in being attached to the Lord Glorified in the
Scriptures [like Prahlāda e.g.].
Also, in the episode of Ajamila which Shukadeva describes as an ancient incident. itihāsaṁ purātanam(SB 6.1.20):
SB 6.3.29:(Yama to Yamadutas in Ajamila episode) They who run from the
truth and fail in their duties unto Lord Viṣṇu, they whose tongues
never express the names and qualities of the Supreme Lord, who do not
carry Him in their heart or remember His lotus feet and not
even once bowed their heads to Kṛṣṇa, bring them all before me.
SB 6.3.33: He who holds on to the honey of Kṛṣṇa's lotus feet,
will not again desire to enjoy the illusory quality of nature [māyā]
that brings distress. Anyone else however, who enchanted by lust tries
to do something to cleanse the passion out of his soul, will surely
find the passion reappear.
Here is the story of Indra-Vrttasura episode where Vishwarupa says to Indra about some prayers..
Since, war between Vrittasura and Indra happened in Treta yuga at the beginning of manvantara, it is long before Krishna descended.
SB 6.10.16: What followed was a great and most ferocious battle between the Sura, the divine hordes and the Asura, the demoniac hordes, that took place at the bank of the [celestial] Narmadâ river at the onset of the first millennium [the Vaivasvata-manvantara]'s Tretâ-yuga.
The event took in Treta yuga of 1st cycle of 4 yugas and we are currently in 28th cycle of 4 yugas in which Krishna descended.
SB 6.8.20: May Keśava protect me with His club during the hours after
may Govinda holding His flute protect me early in the morning, may Nārāyaṇa, the Lord of all potencies, protect me late in the morning
and may Lord Viṣṇu, the ruler with the disc in His hand, protect me
during the hours at noon.
The celebrated Prahlada also meditated on Krishna as is evident from Bhagavatam and Vishnu Purana:
nyasta-krīḍanako bālo jaḍavat tan-manastayā kṛṣṇa-graha-gṛhītātmā na
veda jagad īdṛśam
SB 7.4.37: As a small boy he, in his full absorption in the attraction
of Krishna, refrained from playing and seemed to be absentminded,
having no understanding for worldly matters.
This chapter of Vishnu Purana also says:
Hiraṇyakaśipu, highly exasperated, commanded the serpents to fall upon
his disobedient and insane son, and bite him to death with their
envenomed fangs: and thereupon the great snakes Kuhaka, Takṣaka, and
Andhaka, charged with fatal poison, bit the prince in every part of
his body; but he, with thoughts immovably fixed on Kṛṣṇa, felt no pain
from their wounds, being immersed in rapturous recollections of that
The young prince was then assailed by the elephants of the skies, as
vast as mountain peaks; cast down upon the earth, and trampled on, and
gored by their tusks: but he continued to call to mind Govinda,
and the tusks of the elephants were blunted against his breast.
“Behold,” he said to his father, “the tusks of the elephants, as hard
as adamant, are blunted; but this is not by any strength of mine:
calling upon Janārddana is my defence against such fearful
But Prahlāda, beholding them perish, hastily appealed to Kṛṣṇa, the eternal, for succour, and said, “Oh Janārddana! who art every
where, the creator and substance of the world, preserve these Brahmans
from this magical and insupportable fire. As thou art Viṣṇu, present
in all creatures, and the protector of the world, so let these priests
be restored to life. If, whilst devoted to the omnipresent Viṣṇu, I
think no sinful resentment against my foes, let these priests be
restored to life. If those who have come to slay me, those by whom
poison was given me, the fire that would have burned, the elephants
that would have crushed, and snakes that would have stung me, have
been regarded by me as friends; if I have been unshaken in soul, and
am without fault in thy sight; then, I implore thee, let these, the
priests of the Asuras, be now restored to life.”
Also, 87th chapter recounts an ancient conversation that took place between Narayana Rsi and Narada. This chapter has prayers of personified Vedas.
tasmai hy avocad bhagavān ṛṣīṇāṁ śṛṇvatām idam yo brahma-vādaḥ
10.87.8: As the seers were listening the Supreme Lord related the following ancient discussion about the Absolute Truth that took place
between the inhabitants of Janaloka [the world of the celibate
At the end of the meeting, Narada received some instructions from Narayana Rsi and then he after due contemplation, offered a prayer that is the nectar he extracted from what he just heard from Narayana Rsi.
10.87.45: Śrī Śuka said: 'The self-possessed ṛṣi, thus receiving the command of the sage, accepted it faithfully, oh King. Now completely
being of success he, whose vow was as firm as a kṣatriya's, after due
consideraton said the following.
namas tasmai bhagavate
yo dhatte sarva-bhūtānām
10.87.46: Śrī Nārada said: 'My obeisances to Him, the Supreme Lord Kṛṣṇa of a spotless renown, who manifests His attractive expansions
for the liberation of all living beings
Here, the description is an ancient one and Narada just offered a prayer after hearing fron Narayana Rsi. The meeting b/w Narada and Narayana Rsi happened in the 3rd part of Dwapara yuga. But, whether it happened before Krishna's descent or not is not clear.