I remember 40 years ago I'd open up a Ford transmission pan and find a dreidel looking thing in the pan. The first time took me by surprise.
little plastic plug thing laying in the pan?
i believe they put those in up until the last 90's early 2000's a plug at the transmission/dipstick tube to keep debris out till it was assembled and then it would just get pushed into the pan and would stay there harmlessly until the first pan drop/filter change.
it was a way to tell on a vehicle that you have if the filter had ever been changed before or not if it was still laying in there