I am told that under the old CAR5 low level training was a one-off and it was perpetual
Under the old CARs or for that matter no CASA issued Low Level Certificate.
However, CASA could issue a Permit against the requirements of CAR 157(4)(b) with a condition that the pilot conducting operations in accordance with the provisions of the Permit had to undergo training as detailed the company OM.
As there was no training syllabus published by CASA as such the first 5 hours of the mustering approval syllabus was considered suitable and was either referenced as the syllabus or the syllabus included in the OM and a company "Low Flying Training Certificate" issued.
One could argue that this Certificate would only be applicable while the pilot was employed by the Operator as the training was in accordance with the Operator's syllabus.
In theory, a pilot who had an AG Rating issued under the CAO or the equivalent under Part 137, could not conduct a photography flight at low level as that pilot's training would not be in accordance with the OM unless the OM made provision for this.
I have not read or not am I interested in the machinations of Part 61.
I will leave that to those still active in the industry.