I would tend to follow a "shipping guideline" from ammo shipped to a distributor.  You know.... Brownells orders a pallet of Winc. 5.56 kinda thing.

First, keep it off the floor... IE a pallet or such, and especially if the floor is concrete.  Just to avoid possible moisture transfer, and allow movement of air around the stacked ammo...etc.

Next I would tend to think the cases of ammo should be staggered across each other.... not just stacked like a deck of playing cards.
Possibly leaving a little space between the cases sides.. again to allow air flow to remove any moisture.

And I don't think I would go much higher than 5-6 cardboard  1K rd cases.

Another thing to consider is who made the cases.. I realize that sounds stupid, but foreign made ammo will most likely use the cheapest cardboard cases possible.
On the flip side, some domestic manufacturers use wildly stout cardboard cases ( Black Hills )

So that could factor in to my stacking "plan".

May I ask where you are stacking all your ammo fort ? ... Is it climate controlled ?  That would also factor into how I would stack it.


And if you are truly worried about it "might be to late"... I would certainly ( and grudgingly ) pull a "worse case" to check for 100% function , etc.
Sorry for making you unstack the fort... but it clearly is worrying your mind, so maybe consider it a price to pay for being ammo ready.