Its likely that its a different address for this mode but could be same for wach box.I tried using the All items in box for Resident Evil Remake inside the Real Survivor mode, and turns out that it doesn't work in it.
In the normal game, the code works fine, but in Real Survivor it doesn't.
I suspect that this is caused because Real Survivor doesn't link the item boxes (each item box is a different one on its own), so that could very likely be the cause.
Maybe making a specific All items in box for Real Survivor for the item box under the stairs at the east wing or west wing could do it.
Id have to get a complete save in order to check it.