I agree they probably were not hurt from being a bit low, as long as the 'meat' remained covered... More of a probability that they were not kept charged up, and a discharged battery has some of it's life drained away...
OP - Not much you can do about this now, but for others buying a rig that has been on a lot for a period of time, I recommend you always do an 'independent' inspection of the batteries. Cell by cell - before purchase is completed. If bad, then a condition of the sell is a replacement of 'all' the batteries, to keep them 'matched'. And, specify the exact battery to use. I've known others that had bad OEM Interstates, and replaced them with Lifeline AGM's - paying the difference in prices.
OP - If the coach has a warranty. Do the Cell by Cell test, and if bad, get it replaced now while you can.
We too had the fill system in our previous Bounder, sure made maintenance easier!
Best to all,
Smitty