The cure for this is dates written by you on the package. I don’t have a mongo freezer; just an ordinary side by side in the kitchen.
But I do have a mongo pantry. Every item that goes into it gets year & month written on it with magic marker. Every can, every package of potato chips, every bottle of spice or sauce.
To the degree possible, the new stuff goes in back so the stuff in front is the newest. But every now and then I grab 3 cans of diced tomatoes or whatever and find 2 from last month and one from 3 years ago. Oops.
Doing organized FIFO in a freezer is hard, especially if you’re repackaging stuff, like leftover ham bones saved for stock. But human readable dated labels are your friend.
The other big friend, unless you live out at the end of a very long logistics problem, is to not own 2 years’ worth of perishable food. Own 2-4 weeks’ worth. That makes the size of the problem manageable for the amount of effort you’re willing to put into it.
Right now I have 3 roasts, 3 sets of ribs, a half dozen steaks, and a half dozen pork chops in there. Plus a couple servings each of fish & of shrimp, and about 6 frozen containers of two different stews I made a couple weeks ago. 3 or 4 kinds of frozen veg, and a couple kinds of ice cream.
That inventory is off the top of my head. The counts are not guaranteed to be accurate, but they’re kinda close. The oldest roast is about 4 months old now and overdue to be cooked. Probably later this week.
That’s a manageable problem. If you’ve got 400# of frozen stuff, unless you also own a platoon of mouths to feed you’re making your life harder, not easier, with all that stuff.
Good luck whatever you do. Keep us posted if you have a breakthrough!