Here are all the corresponding versions:

BBIS = BBCRM/BBDM
6.15 = 2.5
6.20 = 2.6
6.25 = 2.7
6.35 = 2.9
6.40 = 2.91
6.45 = 2.93
6.50 = 2.94
6.53 = 3.0
6.64 = 4.0