I dug out the Standard Catalog and found that the square-butt 629-3 was produced 1989 through 1992. Some early 629-4's (1993+) may have been square butt until the switch to round butt production only in 1996.
Now, let's mix it up a bit.
The 629-2 Mountain Revolver (1989) is round butt.
The 629-3 Classic series (1990) are all round butt.
My conclusion.
There _may_ be a round butt 629-3 with standard lug barrel out there. Maybe.
There _may_ be a square butt 629-4 with standard lug barrel out there. Probably.