Wasn't FDR validation testing one of the aspects picked up on by the post accident audit? The FDR had to be periodically tested to ensure that all parameters were being recorded, I don't think Bristow had been doing this. I'd be surprised if there had been any undue interference with the data before the FDR had been shipped to the UK; probably just lack of maintenance oversight that it wasn't working properly.
Please bare in mind that some operators have been flying S76 safely for 35 years without a single accident. Safe operation depends on the pilots flying them and the mechanics maintaining them. If there was an inherent flaw in the S76 flight control system design then loss of control accidents would be more prevalent than what history shows.
I'm sure they'll be able to unravel the circumstances of what happened to the Bristow accident despite not having a full set of FDR data. I still suspect there was an electrical gremlin that suckered the crew into thinking they had a flight control mechanical problem.