Ok people BBS is set 10 years before KH1 right, at the end of BBS we know who xehanort is. It's said that Xehanort was Ansem's apprentice for a FEW YEARS, in that time, xigbar could have got scratched and lost an eye, and Ienzo grew up. The chamber was built, the key hole of radiant garden was found, Kairi was sent away to destiny islands and then either they became nobodies and sent AtW away or they sent AtW away then became nobodies.
There's a large time span, remember BBS story is 10 years before KH but what goes after the game's story ends could be explain in the video afterwards such as the credits (like KH2).
Here's a time line:
|------------|----------------------------------------------------------------------------------------------|<- long time gap for anything to happen in time.
1. beginning of bbs(at the end of the 10 year span
2. end of bbs posibbly a year or half a year
3. KH1, there's a long time gap for anything to happen. The heart research has to be done, which has to have xehanort, who is at the end of the game (as speculated). Mickey also has to be king, nomura did hint that maybe mickey isnt a king in BBS