It may have been charged at 13.2, to 13.2, or whatever you want to call
it. But if you're taking the measurement right after charging, you're
reading an artificially high voltage.

No, there's nothing "artificial" about it.
That's the voltage reading at the time a battery finishes charging. As others
have said, (quoting various time periods from
"almost right away" to "overnight") the voltage eventually drops to a lower
point.

If you've got a $3000 paycheck, spend $200 on the way home from work and only
have $2800 with which to pay your bills, would that mean that you *never* had
$3000?

If you put the battery to work as soon as it has recharged to full capacity and
before it undergoes the internal changes that lower the voltage, you can take
advantage of (some of) the additional voltage.

A battery that cannot be brought to a point above 12.6 when charging,
considering the benefits of the internal heat and the concentration of
chemicals on the plates,
is not in good shape. What would happen to the battery that barely charges to
12.6?
It will also cool down, the chemicals will also equalize, etc.......leaving you
with
what? 12.1? 12.2?

If we are going to apply the "battery cools down and chemicals equalize after
charging" caveat to the battery charged to
2.2 volts per cell, it must also be applied to
batteries charged to only 2.1.