This morning, I looked at the bubbler valves and it looks like somethings happening, because both of the jars/DJ's of the Apple and Blackberry are much more active i.e. I can see a fair amount of "micro-bubbles" coming to the surface of the wines and the valves are bubbling much more regularly.
Though I still don't see how it might be lack of nutrient that has caused this, especially with apple juice and frozen blackberries. Of course, it'll be something that I've missed, not tested for or just not thought about, but it does seem a little weird.
I think I'll have to dig out the data sheet on the yeast - though whether that'll give me anything to go on, I don't know.
It does still strike me as strange because the jar that was racked still has a much higher gravity, though it doesn't have the considerable layer of sediment of the one that was racked (wrongly) last week and I wouldn't have thought that the "top off" of the cheapo supermarket apple juice would have raised the gravity by 20 points - it's "only juice" after all, it has no added sugar etc.