A State Historic Marker

In 1987, the state of North Carolina installed a historic marker commemorating the Blue Ridge Parkway near Low Gap, North Carolina. The marker unequivocally states that the Parkway construction began on September 11, 1935, a date that has generally been understood to be the Parkway's "anniversary."

This date has rarely been questioned or qualified in public writings about the Parkway. Rarely does anyone ask: What is meant by "began"? When does a project as large and complicated as this "begin"?

Is it when the project idea is first floated in public?

Is it when the project is approved by some official entity?

Is it when funding is released?

Is it when a contract is let?

Is it when someone turns a shovel of dirt?

Records about Parkway history present all of the options above. The anniversary could reasonably have been pegged at a number of dates between 1933 and 1935. 

Even if you consider the sign's designation of the start of "construction" as the key marker, things get confused.

Is it possible to peg a true beginning date of a project this size? What are the implications of doing so. Or not doing so?