Thanks for the write-up, well done! Most of the information I did already know about, but some small details not yet, so nice to be able to fill in the gaps. 
Also good to see @PocketCreacher already found this article, since he contacted me about some of my comments/threads where I mentioned Sameji.
In case you want to add more signature examples to your list, here are mine:
Date is also 2000.2.20, thus Sapporo Champion Road 2000 as mentioned in your list.
2000.1.9 (January 9th, 2000) - first day of the Champion Road 2000 tournament, which ran from January 9th to February 20th, 2000. (EDIT: Which I see is also already in your list as Nagoya Champion Road 2000.)
1999.8.4 (August 4th, 1999) - Challenge Road Summer 1999 event at the Kantō conference in Tokyo International Exhibition Center (Tokyo).
And I also have the signatures of the Steel- and Dark-type researchers:
Both of the cards are dated 99.12.19 (December 19th, 1999), which was the day of the Doduo Tag Match Corner event, a parent-child Pokémon card tournament in the Official Pokémon Card Gym of Osaka. The top post in this Japanese blog briefly mentions this event and it also has a photo of the female Steel-Type researcher who’s autograph you can see on the right in the picture below (I have yet to see any picture of the male Dark-Type researcher). This Doduo Tag Match Corner was one of the Challenge Road 1999 side events that were briefly mentioned in this Pokumon article.
These and more autographed cards can be found in this post of my collection thread (although I still have to update it with all the autographed cards I added after I made that post).
PS: Some of the pictures within the spoiler tag mention '00 as year, rather than written out 2000 you have in your table above it. Since you’ve added the written out date as third column anyway, I think it’s better if the second column contains the '00 instead of 2000. Just my 2c, though.
Greetz,
Quuador