Unregistered BAS service providers who are acting under "supervision" in any form cannot advertise that they can provide BAS services according to our discussion with the TPB.
The TPB does not accept loose comments like "reviewed by a registered agent", or even "supervised by a registered BAS agent".
In order for a bookkeeper who is not yet registered to get those hours and advertise their services, the actual supervising agent would have to be named, according the TPB chairman Ian Taylor. For example, something like "BAS services are provided by ABC Bookkeeping, BAS Agent number 1234567". In this case, the supervising agent would have to consent to their name being quoted in the ad.
So there in no "P" plate system and no exceptions for being supervised. Only a registered agent can advertise BAS services; if a bookkeeper is not yet registered they cannot advertise BAS services under their own name.
Note: I do think it is acceptable to advertise that you are supervised and am pleased that the TPB agrees with our view that the supervisor has to be specifically named.