If one stops the run soon enough then it may never make a difference. Lots of us noobs "run it till it stops" and will always notice the dreaded gradual slow-down and if take the time to check the same cells will always be hotter after the run AND after the charge.

The weak cells in a sense "are getting it from both ends" during charge slightly overcharge and/or during discharge slight cell reversal. It may make the weakest cells get weaker at a faster rate than the strong ones and a lot of times it is the center cells in a pack.

I'm still not sure how much reversal hurts, but even at a tiny rate when the cell is empty it is empty and will be reversed. The key is how much the cells in a given pack are matched/balanced and the voltage cut-off point. All these tests are done at a cut-off that is much lower than the norm.

I'll break into the 4 spidery looking mec packs soon.