But isn't the point of the pokedex to fill it yourself? If it
already has the Pokemon shown and the number then you defeat the
purpose.
It's supposed to be a mystery, even though most of us know already,
what Pokemon is next in the pokedex. We are filling it out for
Prof. Oak Rowan, so it wouldn't make sense for numbers
and Pokemon to already be filled in that we don't have.
If you're really curious as to what is missing, you can goggle the
number of the missing Pokemon or google the region's pokedex and
see what you're missing. The most common site to look up Pokemon
information can be found here at Bulbapedia. An example of a filled Kalos Pokedex for example can be found there.
So if you're wondering what you're missing, you can check there for
all the regions so far.