Many moons ago, I posted a question that ran kinda
like this:

"If you got more than one Fire Stone, would the
effect be cumulative"

I was told to try it myself.

I did.

It isn't.

Maybe my game is glitchy (it is second-hand and
GameShark ravaged) but I emptied my items
completely, found a full stock of Fire Stones, and
my monster still wore out at the same rate
as before.

Note: The point I tried this, I had only 10
stones.

Like I said, my game may have just glitched out...

Good work. I'd say it's pretty conclusive.