"industrial machines undergo almost constant refinement/tweaking as new technologies become available/affordable, so there may never be a "final" design....."
I doubt that is true. Industrial machines have a capital value on the books that is depreciated for accounting purposes, probably at 40%. The whole purpose of a capital project (of which the P2O machines are) is to produce a revenue-producing asset on the books. There are other kinds of projects, like those that are just expenses (cleaning up an environmental mess), but most are capital.
Last time I looked, JBI P&E was worth 4.5 Million on The Balance Sheet.
As time goes by, the asset becomes worth less, which is a nice expense to have, but makes no practical sense. That is why in Business School we used to add the depreciation back on when doing Pro Forma statements on. An industrial machine, properly maintained, can operate far beyond what one would consider normal. Nuclear plants in Ontario have been operating since the 1960s and are still going. When built, they had a lifespan of maybe 20 years. With proper Preventive Maintenance, they simply do not degrade or wear out.
So the point is to build a machine, then use it until it is no longer profitable or not environmentally friendly.
Tweaking or modifying a machine is not part of the normal operating environment. That is why the point of a capital project is to get the asset on-line as quickly as possible. Schedule slippage is not tolerated.
That is not to say that enhancement projects do not exist. They do. They also add to the capital value of the asset.
The asset is taken down (inoperative) for periods of time to allow for preventive maintenance, and for the execution of projects to enhance their operations. That is normal. But, these are shutdown windows of a few weeks at the most.
Endless tweaking or modifying is R&D work.
We hope it is not when... 
