Is there any prevalent philosophy regarding how many “initial worlds” exist in Everettian style “Many Worlds“ theories?

If I understand the general concept correctly, in the context of the Everettian “Many-Worlds interpretation” of QM, as opposed to seeing the wavefunction of some quantum process collapse and result in the realization of one of the possible and physically permissible outcomes to the exclusion of the other physically permissible outcome(s), it is posited that all physically permissible outcomes are realized. That of which is to say that the initial world which exists prior to a quantum measurement is “split” into multiple new worlds or branches, each of which given more or less credence based upon how likely or unlikely the measurement that outcome is. A single initial world is branched into many new worlds.

With that in mind, is there any prevalent philosophy amongst Everettians as to how many worlds existed “initially”? In other words, is the general view that all of the possible worlds that exist at any given “time” can all be traced back to some initial “meta-world” (for lack of a better term)?

I get that there are, for all intents and purposes, no ways by which to verify, observe, or disprove which worlds do or don’t exist or their Providence. Rather, do subscribers to the MWI think that the concept implies the number of inital worlds before the first possible quantum outcome or branching? Or is there no such thing as “before the first possible quantum outcome or branching”?