Hi, I am trying to study his game because I want to learn more about his endgame, particularly the boundary plays. I want to know which one of his games demonstrate such plays, or what years in his career did he play his most excellent endgame.

You could use the below to find his successful years in international tournaments.
http://homepage.ntlworld.com/andrew.j.s ... Table.html

There is a book by Slate and Shell: http://www.slateandshell.com/SSYZ005.html

The first game in the book is Lee vs Rin Kaio in the Tong Yang Securities Cup (5th game). That should be Lees first title. I hope that helps.

There's a dated Chinese book that covers his international tournament games, 李昌鎬世界冠軍激戰譜 Lee Chang Ho: Highlights of the International Competitions. Publisher link here.

Here are the titles they've chosen -- should note that he didn't win all of them:
1. 3rd Tong Yang Securities Cup (1992)
2. 4th Tong Yang Securities Cup (1993)
3. 7th Tong Yang Securities Cup (1996)
4. 9th Fujitsu Cup (1996)
5. 1st LG Cup (1997)
6. 2nd Samsung Cup (1997)
7. 11th Fujitsu Cup (1998)
8. 9th Tong Yang Securities Cup (1998)
9. 3rd Samsung Cup (1998)
10. 3rd LG Cup (1999)
11. 4th Samsung Cup (1999)
12. 1st Chunlan Cup (1999)
13. 4th Ing Cup (2000)
14. 5th LG Cup (2001)
15. 7th LG Cup (2003)
16. 1st Toyota-Denso Cup (2003)
17. 4th Chunlan Cup (2003)
18. 8th LG Cup (2004)