Shelly, I am not an expert on sherry or port at all, but I have had 2 or 3 bottles open since my 40th birthday 8 years ago and we are still drinking them. Ill advised, I know but the flavor is still good. I have heard that optimally, it shouldn't be kept open for more than a few weeks.
I love the new bitters, er absinthe, bottles and the Opaline has a lovely color. The St. George's is less pretty, but I like the idea of dashing properly.