I think this sentence is the core of your confusion. You can apply any
voltage you want on the battery. "Equalization" or "Reconditioning" modes
of chargers often apply 17 volts, and the battery will rise to that
potential. It will also boil and melt if you leave it there too long.

17 volts is overcharged. "Equalization"
involves the short term overcharge of a battery to blow the crud off the
plates, but it is not a charge that a battery can sustain for a long period- as
you correctly note.

13.2 is the proper reading for a fully charged battery. That is the level which
any decent charger will maintain, and there is no "overcharged" condition.

There is a serious difference between a fully charged reading of 13.2 and an
equalization charge.