You bring up good pionts.  As usual, I find your broad base of knowledge/experience, very informative.  Thank you.
Yes, I do keep batteries in many of the flashlights around the house and they are used very infrequently.  I try to keep them "at the ready" and as such, do keep them filled with batteries.
I too have never found a loose battery that has leaked, so there is a tie in.  I have a few flashlights in the car and have not seen a problem there, but perhaps it is just an accident waiting to happen.  If I recall correctly,  most of the corroded batteries were Eveready.  Perhaps some Duracell.  I imagine that even with the lights turned off (pushbutton) there is some leakage.  That, coupled with minimum usage, could be the recipe for disaster.
As a side note, the G2Z I ordered after reading the notes arrived today with all the accessories as well.  What a light!  But, at about $90, I will be paranoid about losing it.  I find the cases to carry the extra bulb assemblies to be a bit bulky, but I assume they will serve their purpose very well.   The light and bulb storage cases each come with a lanyard, so no reason to order a separate lanyard.
Nice choice all the way around.