Wills, I don't understand the physics or biology of it either, but it seems that pups are usually more vigorous than the mother plant -- when the mother was the original planting. For example, the first pup ("first ratoon crop") almost always gets taller than the mother plant. You can see many examples of this in the data on MGIS:
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In my local nursery, you can see many cases where the mother stem died before blooming, yet the pups seem quite healthy.