Some data to go with my note above. (Please excuse the crudity of this model. I didn't have time to build it to scale or paint it.)
This is data from one of 057's customer vehicles in the extended service plan program (shared with permission). A very early 2013 S. This is data from a couple of weeks ago. Our monitoring device, using the data above along with other data used internally on the device, determined that the car was going to eventually throw some errors related to an SoC imbalance. The customer was notified, and they were actually already in the middle of a small road trip.
"Imbalance? But wk057, that pack looks very well balanced! Only off by 5mV!" Ah yes, the myth of voltage being the end-all-be-all of balancing. NOPE.
Check out the capacity of some of the groups in the front hump. Notice anything? One of these things is not like the other....
Other data suggests this is the "standard" moisture issue with these older packs.
Sure enough, near the end of their trip, the car threw the "Maximum Charge Level Reduced" error, as the SoC imbalance grew beyond the BMS's ability to handle. (Fortunately, all is well and they managed to make it home. The car is en-route to us for a pack replacement.) Letting the car sit for weeks can temporarily resolve some of the presentations of this error by giving the BMS time to catch up with the capacity delta, but with use it will always end up back in a position where it can't keep up and will have to severely limit charge levels and discharge rates.... right up to the point where you can't drive anymore.
To Tesla's credit, in much older firmware you would have just been left stranded instead of the BMS just reducing usable capacity and power.