I had one bottle each remaining of Hardy's Coonawarra Cabernet Sauvignon 1991 and Ravenswood Sonoma County Zinfandel 1991. These both are rather basic wines from the mentioned companies. However both have aged very well and remain in good condition. Both wines were properly stored since release.
The Hardy's CS is still rather deep in color with only little evidence of age. It has plenty of acid and has now smoothed. There is strong cassis with much spice character - nearly as if it contained some Shiraz. Although not a gold medal wine, it was much better than expected for a basic wine and well suited for less formal drinking.
The Ravenswood Zinfandel was still quite dark with not much age showing. It had thrown some crust that stuck to the side of the bottle that had been down on storage, and the crust was nearly black. The alcohol content was listed as about 14.3%. Although not a late harvest style, it was a quite full food style of wine. There was ample acidity, and the wine had smoothed well. The typical Zinfandel dark fruit character remained along with considerable spice. This is not as complex as some of Ravenswood's top level wines, but it is very good indeed and is holding well at an age at which many other Zinfandels hav lost most of their fruit.
Both wines cost under $US 10 on release. Of course the price today would be considerably higher. Although the higher level wines from these companies are more likely to age better and longer, even the basic level wines can keep fairly well in certain years.