Is one logical way, if you count in this way 10th generation is possible:
1/ EOS-1 (1989)
2/ EOS-1N and 1N HS (1994)
3/ EOS-1NRS (1995)
4/ EOS-1V and 1V HS (2000)
5/ EOS-1D (2001) and EOS-1Ds (2002)
6/ EOS-1D MkII (2004) and EOS-1Ds MkII (2004
7/ EOS-1D MkIIn (2005)
8/ EOS-1D MkIII (2007) and...