Dear Robert,
The local blade azimuth angle output from AeroDyn v15 does not use AzimB1Up, which is only defined/used in ElastoDyn. Instead, in AeroDyn v15, the local blade azimuth angle is defined based on how the rotor disk-averaged relative projects onto the disk (based on the skew angle between the rotor axis and inflow). Please see the following forum topic for more discussion on this: Azimuth Angle of the Blade - #10 by Jason.Jonkman.
Best regards,