I still have a couple cans of ATF in the garage that are still in the cardboard cans. I really don’t know if the stuff inside is good anymore. I bought them in the mid 80’s, that is about the time oil switched over to plastic bottles.
Can’t answer the first question. Hardly seems to have been twenty years, but I suppose it has.
The other question is interesting. Cardboard/metal would, of course, deteriorate more quickly. But that means the residual oil in the container would get into the environment faster. So in this context, plastic containers (if closed tightly) might be preferable.
I have an old plastic funnel that was designed to fit the top of an oil can. I still use it when adding oil.
My dad had one that I liked. It was a metal funnel on a metal handle that was bent into a sort of a pistol grip. There was a lever/trigger that could be grasped by the fingers and squeezed. The can was placed onto a sheet-metal support above the funnel, and the spout was put into the engine. Squeezing the lever forced the can into the piercing blade, and the oil flowed into the engine. Dad kept it in its original plastic bag to keep the desert dust and sand out of it.
OTOH plastic containers may not be capped, and whether or not they were they would likely rupture when buried in a landfill. Obviously plastic bottles can be recycled; but the number of plastic oil bottles I’ve seen going into recycle bins is exactly zero.
I put oil cans in the recycling once, and the garbage crew left them with a note saying that they couldn’t take them. The parts store around the corner collects in a bin beside the recycled oil tank.