https://www.slab.org.uk/guidance/payment-for-diagnostic-work-where-standard-aa-later-becomes-available/
If, after you have approved and provided advice and assistance by way of a diagnostic interview, we agree with you that standard advice and assistance should be available: standard advice and assistance is effectively substituted for the diagnostic interview;
In these circumstances you lodge one account for all the work undertaken from the date you admitted the client to advice and assistance.
The effect of this is that you are entitled to provide a further diagnostic interview if your client seeks this within three months from the commencement of the previous advice and assistance (subject, of course, to the advice being reasonable and appropriate).