If you were working with topnotch AGMs my eyelids would not be heavy.
Now that you have fixed reference points (you should do voltage / percentage references...
If they start losing those characteristics way down the road, you will know for sure. Something tells me your battery of interest entered your domain at a lower voltage.
Fixing basic references (not nearly as all consuming as what you did) makes future exams a snap. The first thing I did with my Lifelines was to measure voltage as arrived. Both were above 13.00 volts.
Hitchem to the yoke and makem pull the plow BFL!
That's what they're supposed to do for a living.