You may be suprised, some quality LifePo4 cells like A123 (used in Dewalt tools and hospitals) take can an amazing amount of abuse, you dont really need a BMS with them for small batteries, and you can charge them with a standard car charger if you need to.
If the final few volts you used were low amperage, and it was not for too long, your probably fine. They are not like Li—on cells that burst into flames when they get over charged.
My test battery made of A123 cells have been really low and really high at times and still work like new.
Remember, 4.2v is still within spec for LifePO4.
Time will tell, but if it was only briefly, there is no swelling and they didnt get hot, your probably fine.