I’ve never come across big end bolts that are tightened to the yield point, so unless damaged, they should be re-usable on all but the most highly stressed engines (Formula 1, etc?). That said, we all(?) know that the rod bolts on early 310 engines were not up to the job!
Clearly someone has been in your engine previously and ‘mixed and matched’ parts. ‘Nuff said?
Personally, I can't ever remember changing any rod bolts in the several dozen engines I have rebuilt but I have always changed nyloc nuts - and given them a dab of loctite for good measure. BTW get the right grade of nut for the job.
One question might be: Do you add on the torque necessary to run the nut down the bolt threads to the tightening torque specified for the bolt?🙂