I haven't read all of the above, but a couple quick points.

John, you didn't state the definition quite correctly. Rather than being the ratio of cycles to failure, it is the ratio of nominal stress in the components, for the same number of cycles to failure.

Nominal stress is the nominal stress in the matching pipe, a M/Z calc where Z is the section modulus of matching pipe.

So, first, if you do an FEA on a component, you need to know what the matching pipe is to get a ratio to get the SIF. The second consideration is that due to the fact that the ratio in the codes is relative to girth welded straight pipe, there is another factor of two. So, for example, if you did an FEA of an elbow, you would have to divide the highest stress calculated (primary plus secondary plus peak in Div 2 terms) by two, and then divide that result by what the stress would be for the same moment in matching straight pipe.

This is very commonly misunderstood and very commonly done wrong, including in published papers.