If you look at it that way than these labors were being processed in atleaset 20 centers but still such huge Backlog was created and it took them years before they realized they need to do something. And everybody knows what they did !!!! they created more chaos, seeked more documents, looked more stupid(45 days letter is a perfect example) created further backlogs and more backlogs for 1000s for whom dates were pretty much okay.
so number of center is not what counts, what counts is how much prepared they are to handle this kind of volume. And as legal immigration in not on wish list of U.S. government right now, I will be surprised if they have any plans for handling this kind of volume when they get it.