Disclaimer: This information is collected through illustrators listed in TCG cards, bulbapedia and observational analysis made by myself, since much of the information regarding official art is not published. So there might be errors. Ken Sugimori is also still working on both pokemon and human characters for the series, so he is likely behind many designs that are simply illustrated by someone else. He should still not be credited for work he did not do.
Decided to expand on my thoughts about people praising Sugimori for having improved his art over the years. While it’s entirely true that he is much better than he used to, the examples shared in posts like that are 90% of the time not drawn by Sugimori at all. So let’s stop spreading misinformation as the differences in art style can be easily pointed out.