epilogue:
Although the original OEM AC/Delco continued to test good, and performed without further incident for the last week, I replaced it on Sunday with a new Wal Mart Maxx battery.
The clincher was finding more corrosion product under the negative battery terminal, even though it had been cleaned a few days previous. It appears to be venting around the negative post.
At full SOC, the Maxx tested at 12.81 volts under standby load in the car, and had 3.63 megohm internal impedance. CCA tested at 785, on a rating of 650 CCA.
The old OEM Delco went out at 12.75 terminal voltage, 6.44 megohm impedance, and 434 CCA on a rating of 650 CCA.