Does every Buddha have knowledge of the past, present and future? I quote from the “King of Samādhi” Sutra. First Buddha says “What is the samādhi called the revealed equality of the nature of all phenomena?” Then a bit further down the text he says “It is knowledge of the past. It is knowledge of the future. It is knowledge of the present.”

Is every Buddha omniscient according to this sutra?
Questions about omniscience often arise, but the answers point us to a different knowledge:

MN90:17.4: “Sir, I asked you about omniscience, and you answered.

The Buddha taught us to not get trapped in the net of views worrying about omniscience. The Buddha taught the Four Noble Truths, which apply to the past, present and future for all sentient beings.

DN1:3.72.3: In the same way, all of these ascetics and brahmins who theorize about the past or the future are trapped in the net of these sixty-two grounds, so that wherever they emerge they are caught and trapped in this very net.  The Realized One’s body remains, but his attachment to rebirth has been cut off.  As long as his body remains he will be seen by gods and humans. But when his body breaks up, after life has ended, gods and humans will see him no more.

The Buddha taught us how to escape that net to end suffering. And when pressed on particular points of omniscience, he would teach about the path:

MN90:10.1: “Sir, I am not asking you about the present life, but about the life to come.”
MN90:10.6: “Great king, there are these five factors that support meditation.

And in that teaching, the teaching of the universal knowledge of the Four Noble Truths, the teaching of the knowledge of the Noble Eightfold Path that leads to the end of suffering, we have:

DN28:19.16: “The perfected ones, fully awakened Buddhas of the past and the future are equal to myself when it comes to awakening.”