Yes, IPC-7351C is the standard, IPC-7351B only defined level A whereas revision C also defines level B. You can chose to use Level A or B or use a combination of both but you should also indicate this in your fab documents. Level A seems to be preferred.
The standard is, the zero orientation of a component is as follows:
For two pin components pin 1 is to the left, pin 1 is always the positive pin or the cathode in the case of diodes or LEDs.
For components with more than two pins pin 1 is upper left (Level A) or lower left (Level B).
For components where pin one is not in a corner, such as ICs that have pin 1 at or near the center of one side, pin 1 is to the top.
Here’s a good reference for those who don’t have access to IPC-7351:
Electronic Component Zero Orientation For CAD Library Construction