Ruby Special Reserve Drinking Window?

[Bertie3000]

As a little experiment I recently bought some old bottles of Noval LB (Brightwells for those wondering). I was interested to see how they tasted after something like 50 years in bottle (there is no bottling date but labels/bottles suggest 1960s or early 1970s to me). I just opened the first bottle. There was a small amount of sediment but not much compared to a vintage. There is some fruit (cherry), some sweetness and a nice length. It is certainly fairly simple and at the delicate end of port tasting but is perfectly drinkable and pleasant, especially on a Saturday afternoon. The question I am now interested in is how long can you/should you keep ruby reserves for? Do people have experiences of drinking very old ruby reserve port that has been fantastic drinking?