Goffers,
Both and/or any case of TBO/Finite life can change in the life cycle of most models. It more than likely starts out low as you say then increases with empirical evidence then inevitably it possibly goes down again as MTOW's increase during the life cycle of the type. ATA Chapter 4 and 5 are normally constantly changing.
Or not.
As usual being the customer we probably get about 1% of the real picture.
The "code" written in manufacturer service bulletins between the lines is "priceless" in some cases.
