You can include multiple baselines in a corridor volume calculation, but you should make sure that the assumptions for the volume calculation method are satisfied. That is, the distance (L) must be accurate for all baselines.
The formulas for both the average end area and prismoidal methods calculate corridor shape area based on the distance between sample lines. In the following image, the sample lines are perpendicular to their parent alignment (on the right). While the corridor on the left may be included in the volume calculation, the result will not be accurate because while the distance (L) along the parent baseline satisfies the volume calculation method, the distance along the second baseline does not.
To obtain an accurate volume calculation in this situation, create sample lines along the baselines for both corridors.
For more information, see About Corridor Sections.