In 2004 Markus Wolff (back then chief developer of Klein&Hummel, predecessor of Neumann where he still holds the same position as far as I know) told me about the K&H O300D I wanted to buy, that the woofer would change very slightly in the lowest bass within the first hours. It would be measurable but at the border to being audible. The FR of the whole speaker would not change at all otherwise (the same is true for the optional grille: it's influence on FR can be measured but is inaudible).It does matter in the wider contest. If a driver went through 10 minutes of high SPL QC testing and goes through the same again after producing a complete loudspeaker there is a good chance that the biggest mechanical stifness already is gone.
Somebody from Genelec is active on this forum, lets ask them the question? I forgot his name. But I'm sure he can give some insights on this. Neumann also has people registered here I believe?
I had asked about break in because he had told me that K&H measures every single O300D and stores the parameters of each driver in a data base to be used if a customer wants to update to the external DSP controlled crossover. In this case he needed to tell K&H the serial number of his O300Ds and K&H would program the crossover for them. This procedure would not work if the speakers change significantly after leaving the company.