IMO that depends on how many cells are in parallel and or series.
I would rather have a 4s1p with 3 cells over voltage like 4.25v to make up for a bad one at 4.05 than a 2s1p with a low cell at 4.05v and the other cell at 4.35v.
They can be any amount , as long as no one cell goes out of range. 3.5-4.2 volts.
It depends on the pack , the cell capacity match, and the level of charge and discharge.
An example would be a user who charges to 4.2 volts and discharges to 3.5 resting volts. The cells need to be perfectly matched in order to never go out of range. If at them bottom the pack had a cell that was .1 volts lower then the rest then the minimum for the (2s) pack would be 3.5 + 3.6 = 7.1 volts.