I'm a Vetter fan too.
From the Man's own website I read:
The Windjammer SS was sold March 1977 through the end of 1979, but came with windshield clips beginning 9-77. These were designed to replace the 2 uppermost mounting screws left and right. That change virtually eliminated snapped windshields on these fairings.
The PO probably had it installed at the dealer before he picked up the bike.