Well, they might ended production in 1984, after they made some stock to supply dealers ... I don't think the demand was that high. But it was still made after introduktion of the E30 3 series.
Correct me if I am wrong, but was it not sold an E21 new in Switzerland (or was it Belgium??) in 1986? As the last sold one? I think I have heard that somewhere sometime..
Yes, that is possible, that would be an old car from BMW stock.
For example: i work at a car dealer. Last year we had a facelift of our middle class model. Today, so a year later, we still have 5 of the pre facelift cars in stock ... they are long out of production but unsold factory stock goes to dealers which they will have to sell one way or the other .. so a 1981 produced car can be registered in 1985 ...