Man, the prototype Pokemon designs were so very interesting-I remember that I did a whole whole bunch of 3D sculpts of them back in 2011; the actual art of this thing made by Ken Sugimori's in the bottom right there in the compilation
Oh they kind of do reuse some older designs; like they had this old turtle-Pokemon appear in a gen 2 pamphlet, but it never appeared again in the series, it wasn't until Gen 5 happened that it was repurposed into Tirtouga/Carracosta
Link
ratdust
Damn, this is really good and spot-on to the original.
(I wish they would revisit/reuse some of those old designs...)