B5.1 is used in conjunction with QC1. One way to explain the difference is: B5.1 defines the rock and QC1 certifies it is a rock.
B5.1 defines the qualification of the AWI, WI, and the CWI. It defines the education, experience, job responsibilities, etc. of the three levels of qualification.
QC1 defines how the three levels are certified by AWS and what must be done to maintain the certifications, i.e., the CAWI, CWI, and SCWI. QC1 also defines endorsements and how they can be utilized to maintain the CWI and SCWI certifications.
B5.2 defines the qualifications and certification of in-house visual inspectors. The certification is limited to the contractor's employees and is only valid for inspections performed on behalf of the employer.
I hope that helps.
Al