Interesting thing about polls. They normalize them to the number of Democrats, Independents and Republicans that they think there should be. So let’s (simplify this and)see how this works. Suppose you poll 10 people and 6 are Democrats for Obama and 4 are Republicans for Romney, you call that as Obama 60% - Romney 40%. Then, some time later, you asked those same 10 people the same question and all answer the same except 2 Obama Democrats now say, “We are sick of Obama, we are now Republicans and we support Romney.” You’d think that would be reported as Romney 60% - Obama 40%, BUT NO!!!! It’s reported as “Obama 60% - Romney 40%” because we had previously established that 60% are Democrats and 40% are Republicans and the new poll has to be updated to reflect that same party affiliation.
You’re basically saying that the “normalization” process in polling can hide tectonic shifts in the real numbers because it’s a backward-looking factor.