Multiple NNC for landing performances question
 

If you have multiple non normal conditions ie Eng Fail & Slat Drive the OPT will only take one item.

Previous company said just take the most limiting. Current company has a super complex method of calculating both plus normal landing and then factoring results to give theoretical number thats applicable to your 2 NNC landing.

My question is what does your company do?

Safety first.
Take most limiting option, then add some more to factor in additional errors.
There is no way the OPT can deal with multiple failures just like MEL cannot.

It all depends on what failures you have as they may impact each other or may be isolated cases easily distinguished.
Isolated cases need not necessarily make the problem bigger then the most limiting individual case.
Impacting cases need care and attention, hence my statement above to add some more in those cases especially. How much more is not determinable unless you know what failures are present.

4-bars on the shoulder comes with responsibility to take decisions outside the box when required to do so, it's part of good airmanship.
Some airlines train their cadets to become great masters of SOP, but airmanship is not always taught and cannot be taught by those who haven't been taught anything but SOP.