Michael is right. My senior stress engineers before just use 2 x SIF of 90 deg. since FEA during that time is scarce if not available.

With the tools available now, it's better to use it and compare it to 2 x SIF of deg.

Physical testing is another option but costly and not practical. If I'm not mistaken, these tools are also verified thru physical testing.

But for me, it's a must to have a good fundamental background of FEA before using it. Make your own verification to have confidence in the tool being used.

We have many tools around us as engineers, but in the end, it's not the tool that will stamp the calculations or drawings.