Hi
This is strictly speaking incorrect.
Old firmware versions like 5.1.3 do not support new B-revision APs (JxxxxB). In this case user is entitled to receive for his FW branch a current version that does support those APs. If user buys new MSM430/46x APs, user is entitled to have 5.5.3 which is freely downloadable from HPN support site. If user buys new MSM466-R APs, user is entitled to have 5.7.x.
Where to get a version for B-revision support - contact your local support center.