Whilst people who habitually think in distressing ways are themselves distressing they are at least mostly predictably distressing; people who appear to generally not think in distressing ways who suddenly exhibit a slight suggestion of possibly harbouring one or two distressing points of view or opinions can sometimes seem worse for being stealthed. It occasionally forces re-evaluation of the behaviours previously considered non-distressing which can occasionally be reconfigured as potentially distressing, given that with which they are now suspected to coexist.
If they'd been labelled as they were bought then set B would probably be dead by now, though as they're 2500mAh they're probably a year or two younger than the earliest sets of this type which were a year or two younger than the first generation of AA NiMH rechargeables with which my old cameras were powered, back when bike lights used D cells. I didn't label them until relatively recently, most probably when irritating odd-numbers-of-cell lights started appearing to try and keeps sets together, though there was some inevitable creeping seeing as I wasn't organised enough to always keep them together despite being organised enough to label them in the first place, possibly due to a lack of little plastic holder things to keep them in with the result than a few started to live on their own in random boxes and drawers. I'll have to try and remember to label a recently-bought multipack of AAAs before they escape and split up.