Okay, so the 2016 tech manual also doesn't mention that procedure. The "procedure to recover" is the same trick that Optima recommends for fooling a smart charger into firing up by jumping in a second battery with a higher voltage.The Odyssey procedure is dated March 2016. The Technical manual I have from them is dated September 2016. For completeness, also attached the procedure to recover a deeply discharged battery they emailed me along with the conditioning one.
The reason for getting the documents is one of my PC1400 is apparently weaker than the other (resting voltage 12.65 V vs. 12.8 V), so this is what they thought would help.
But finally, in the battery reconditioning doc, I see an answer as to why the deep discharge and heavy recharge procedure - desulphation.
So instead of doing an EQ, they set a do not exceed voltage of 15v and instead do this deep discharge and recharge with high amperage...hoping that will be enough to blow the sulphation off the plates.
I have seen some reports that it worked for some people, not so well for others.
Did it work on your low battery?