Branadic.....
As noted earlier, General Resistor has made some minor changes in its resistors, that is not uncommon, I also make changes in my resistors, in both of these cases, the internal basic construction has stayed the same, i.e. the bobbin design and lead assemblies have not changed, what we both have done is to make internal changes in the attempt to improve the resistor's performance. Since the interplay of materials in resistor construction is complex, sometimes a 'problem' does not immediately show up and can take months to discover, this is not uncommon either. I did have a problem with epoxy several years ago, that affected only two customers and I replaced both of their orders at no cost, that was one of the problems that did not show up until much later. Where I am located, the humidity is usually not that high and both of those customers were located in much higher humidity locations, the epoxy, despite what the data sheet claimed, had a less than great reaction to the high humidity over time. That of course caused a change in material as one would expect. There has been no further problems. If there has been a manufacturing defect, I have always replaced the parts as any manufacturer should and those have been very limited in number.
My point about qualifications is that I've got over 4 decades of experience, I already know just about every possible failure mode and most of the ways failure is caused, my examination would be based on that experience, I did not intend to infer that you were incapable of analysis as such, just that you are inexperienced in resistor technology compared to me.
If the loss of these two resistors is such a problem I will be happy to replace them at no cost if you're willing to cover postage.....okay? Whether or not the failure was caused by handling or defect.