That is very interesting.
I've been experimenting with names between the 1821 census and 1901 census, just to see the frequency. For instance, I typed in "Thomas Clarke" for both.
1821=>19 hits
1901=> 31 hits
Those numbers seem fairly close in magnitude, but, of course, Ireland and Meath had a significantly larger population back in 1821, when compared with 1901. Also, just eyeballing it, areas seem to definitely be missing.
One of the things I would do if I could go back in time would be to try to preserve the census, silly as it sounds, though I suppose, we should all be thankful for what genealogical records remain.