Nick.
In general, the older canes do provide nutrients to the front. And the atroviolaceum older caness can rebloom.
But I would say to use judgement here. Den atroviolaceum is a very vigorous plant that can produce LOTS of canes. Depending on the size of your plant and how well you are growing it, you could have a very dense & bushy plant with a lot of canes. If that is the case and the old canes are VERY old and shriveled, it might be beneficial to cut off a few canes. This will open up the foliage & give a better presentation.
IF your plant is bushy enough & has enough canes, how many flowers do you really need. I prefer a nice presentation, rather than squeezing every last flower out of a cluttered plant. If your plant does not have as many canes as I imagine, then, by all means, preserve the old canes. But they do reach a point when you do need to cut them off.
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