Any information on this 1968 Port?

So I'm digging around on back of my small cellar and find a forgotten bottle of 1968 Niepoort Colheita - One of the white painted (stenciled) bottles. A little googling gets me to their web site, but their information for Colheita doesn't show a 1968 bottling. The bottle has Niepoort embossed on it along with a seal across the red top. The fill might be down slightly but looks in good shape otherwise.

Any ideas on what to expect when I pop this open??

Thanks,

Mike P