I think that we need to clarify the basics of Punctuated Equilibria (again).
It is necessary to start with the fact that P.E. deals with evolution and Paleontology. The "species" of P.E. are
paleontological species. Thus, changes which do not show in the fossil record or changes which cannot be distinguished from the normal variation within a species are all permitted within "stasis". Since we know of "cryptic species" - biological species which are morphologically identical - it is quite possible that some paleontological species would be considered two distinct biological species if we had living specimens - perhaps some would even be split into three or even more.
The next important fact is that P.E. is a
prediction of evolutionary theory - or to be more precise Mayr's theory of speciation (still felt to be the main mechanism by which new species form). Mayr's mechanism starts with a small population becoming isolated from the main body of a species. Large populations are slow to evolve, by drift or even selection - this smaller population can change far more rapidly. If this smaller population thrives and evolves to form a new species and if it is able to return it may overrun the territory of the ancestral population, giving the appearance of a change more sudden than it actually was. Since most of the evolution happens relatively rapidly (but still "gradually" by human standards) and in a small region it is not uncommon for it to be missed - either absent from the fossil record for one reason or another, or simply not found by us.
Thus Eldredge and Gould's "stasis" is explained by gene flow acting as a stabilising force often restricting the change within successful species - while they remain successful ! - to change within the limits of paleontological species.