The original question was regarding bullets for reloading, not old loaded ammunition. The KKSP was ( and still is) a very reliable bullet at the velocities each was originally loaded at. Their performance was on par with Remington Core- Lokt bullets of the era, easy opening with very reliable expansion and deep bone breaking penetration. These 215 grain .303 bullets are highly valued today to feed some of the early rifles which were designed fot this bullet weight.
Old loaded ammunition is a different story. It can be fine after 50-60-70 years or it can be unreliable or even hazardous. Bang, click, click, pop, click, bang. I have seen quite a lot of old ammo , including some .350 Rem Mag from the 70's, pre war Winchester 30-06 and pre WW1 .280 Ross with split or cracked necks.