In fact, yes, they did have to wait for the airplane to fly. End-plates or winglets were proven before first flight but the problem was the rigging, materials, etc created more drag than they eliminated and thus, were not used.

There are multiple solutions for dealing with the vortice. The endplate is a vertical treatment while the winglets include multiple angles.

This is a quick overview...
www.aoe.vt.edu/~mason/Mason_f/WingletsS04.ppt

First application on Longhorn Lears although concept first proven on USAF KC-135. Later tests using Continental DC-10 also not implemented.

Where you see 'endplates' today is on formula 1 and such.