I've discovered the green cider from showa could be stacked into 201 in one slot, when you put one red cider at the back of them. For example: [green cider x 201] [green cider x 1] [green cider x1] [red cider x 1] Usually the cider takes up 1 slot per item and does not stacks
They stack in 201 even without any other ciders, or any other measures. Its a bug and if you keep them you might have items getting pushed out.
Well since you shouldnt be able too, I guess its not allowed since its a glitch and you would abuse it. You also have the risk of losing items and some other bad things might happen.