gulli
I have always completed a daily inspection which included testing the CV/FDR .... press the tit and ensure the relevant lights extinguish, simple.
I know that maintenance performs an annual test for the authority to ensure the data from the FDR is correct, standard.
The longer term question for the authority, and in this particular instance for Bristow Nigeria maintenance and their safety culture, is how this was not done and why so many individual items failed to record. This is part of the safety system - for everyone, Zero.