Those two are related as "alternative version" in anidb.
Luckily I was able to get good version and watch sak2 recently. Alternative version relation seems to be wrong, since the storylines are not directly releated at all. First series take place iirc in 1920s, second ones in the 21st century.
So "Alternative setting" seems to be accurate enough. ("Characters" could also be an option, but a bit too weak)
[EDIT] [RELATIONS] sak1 - sak2 (aid:88-aid:89)
Moderator: AniDB