Mirror replacement

2000, 1500 series quad cab where the passenger side mirror glass fell out. The replacement mirror has the glass attached to a plastic back where a circle of pins snap into the mirror housing. The circle of pins (snaps) line up with the housing except for three pins, where there is no hole for them to fit, so the mirror can't be installed. The guys at the dealership left me with too much doubt that they knew for sure what were talking about. They are assuming there is a collar that the mirror plugs into, in turn the collar snaps into the housing. My questions are, is there a collar(adaptor) for this mirror, which of course the dealer doesn't sell so a complete mirror must be bought. Did they originally give me a wrong mirror, that had three extra pins that won't fit, or is the mirror they sell a universal mirror, that the different model vehicles may need some of the pins removed for it to snap into place.

Thanks for any help on the matter.