Carlos is correct - use of the term Roundie is indeed a modern descriptor of the 1967-1973 (2-door) cars. If memory serves, I do not recall hearing the term Roundie until the 90's. Having started in the BMW dealership system in the 1970's and subsequently the independent scene in the 80's, we simply referred to the pre-74 cars as round tail light 2002's and the '74 and newer cars as square tail light 2002's.
While undoubtedly affectionate, the term Roundie is just another example of how language and word usage changes through time. I think we all get that.
Older folks, like Carlos (el Chacal) and myself, simply have no use for the term Roundie, or slick-top, or ........
'Round tail-light' suits us just fine ?
1600