hi sometime sun
i am of the camp that strongly suspects that deja vu can be the reliving of a previously experienced moment.
My own personal scheme of understanding is this.....
There may have been in the long distant 'past' a 'first time'. Alternatively it may still be going. First time is the frontier of reality in time. Reality changing into and filling a temporal void.
But first time is 'written' or stored in spacetime. History therefore is also real. BUT history is also susceptible to change and thus becomes a rewrite. ie subsequent time. There can be rewrites of rewrites so that first time history no longer exists in some parts of history. Rewrites are like secondary waves. Ripples that flow across the surface of history. There may be many.
A rewrite wave however does not necessarily change the history it flows over. But sometimes it can. When that happens it might be expected that everything from that point will be different to what went before. A rewrite will flow on a never ending change of history. But consider the life of the sun. Even if the history of man is temporally unstable, such that the history of reality is constantly being rewritten because of man, nevertheless the rewrite may not be enough to avoid the natural death cycle of the sun, and all life in the solar system.
Thus from a grander time scale, a rewrite brought about by people 'frequently' behaving differently in a moment to what they had before, will create change that is restricted in spacetime to before the death of the sun.
By analogy, cultural events can have an inertia in time just like the cycle of a star. Thus say in a war we may act differently in a battle, but the battle is still lost. When we find that a rewrite 'comes back' to the previous history it was rewriting and stops rewriting ....... then we experience deja vu. eg "i remember being ordered to bury this body before".