Emrys wrote:

But I think that the same reasoning would apply whether they have been
cut or about to be cut. As you will no doubt agree flowers/plants
continue to develop/grow a little when they have been cut and placed in
water.

Quite right. The presence of auxins in the growing points (stem tips -
flower stems or leafy stems) is not massively affected if they are cut
from the plant and the same processes continue, albeit on a reducing
scale as the cut material deteriorates.