Sutta AN 1.277 states that “no two Buddhas (Samma Sambuddha) can appear in the world at the same time (without time separation) in a given “world cycle” (for example, during the lifetime of our Solar system).
There have already been four Buddhas (including Buddha Kassapa and Buddha Gotama) during this Maha Kappa (age of our Solar system), and Buddha Maitreya will also appear before this Maha Kappa comes to end. But this is extremely rare; normally there can be many successive Maha Kappa without even a single Buddha.
The relevant verse is :” “Aṭṭhānametaṃ, bhikkhave, anavakāso yaṃ ekissā lokadhātuyā dve arahanto sammāsambuddhā apubbaṃ acarimaṃ uppajjeyyuṃ. Netaṃ ṭhānaṃ vijjati.”
Translated: “Bhikkhus, no two Buddhas can appear in the lokadhatu (world system) at the same time, i.e., without a gap (anavakaso).
The goal of a Buddha is to stop the rebirth process (to stop future suffering). So, of course it was a made-up story by the early Mahayanists that all past Buddhas can re-appear. That is against the very foundation of Buddha Dhamma.