Nick Maclaren wrote:

My experience is that, as with quite a few plants like that (including
many clematis), "must" is wrong - "should" is right. When I cut my
B. globosa (and B. alternifolia) back hard in spring, they flowered
much later than usual, but still flowered that year. I.e. the wood
needs to be of a certain ripeness more than it needs to overwinter.

Which also means that in some years, the growths will not achieve that
degree of maturity. So, if you want a fail-safe method of ensuring a
good show every year, you must do any pruning immediately after
flowering.