Perhaps a little clarification. I believe the Nobile dendros bloom off last year's canes. If this is what you meant by "old", then yes. But canes that have bloomed already rarely rebloom (at least not with type II Nobile types, such as D. anosmum). The canes should never be cut until they dry up completely. I've attached a photo of my anosmum in bud on last year's canes and it shows several years of back bulbs. Yes these are the water/nutrient reservoir and it's common for the very oldest canes to completely be used up and shrivel. These can be trimmed if you don't like the appearance.

If you look at the top of this clump of canes, you'll see several that are yellow. You can also see where I trimmed the bottom shriveled portion off. These are getting pretty much used up as they feed the plant during dormancy. This same principle should be true for type I Nobiles, such as D. nobile, which grow more upright.