SBC's behavior in case of "reg-overload-protect" activated

Hello,

In case of registrations avalanche we noticed following behavior of the SBC: command "show registrations" shows 50000 active registrations, but on next-hop registrar shows only 20000 subscribers with status "registered".  The SBC has "reg-overload-protect" enables, so it temporarily promotes the  hosts, whose first REGISTER was responded with 401, to the trusted allocation (in other words, SBC reserves trusted pipe for their second REGISTER). Due to CPU overload, sipd cannot process all the registration requests that come via both trusted and untrusted pipes, so not all the hosts that got 401 succeeds to register. We need somehow to explain the difference