That is really strange that some have grapes and others do not. What is the varietal of the ones that do and the ones that don't?
It could be possible that the flowers were never pollinated? I assume you have bees where you are?
As far as replacing vines I'd say no for sure. Most vines live...
NO, you should prune no matter how late in the year. I'd say prune everything that is not growing the direction you want, I.E. branches hanging down on VSP and those growing vertical on Top Wire. Try to leave about 26 fruiting branches per vine. If you have a spur that has more than 4...
Andy, In a moderate climate like the Azores has the grapes will loose acidity when allowed to fully ripen, as well as fruitiness. One thing to try is harvest some of the grapes earlier, I.E. 19 brix or so. Don't let them get above 21-22 brix. This will preserve the fruitiness and good acid...