JBL 2441 Diaphragm

Hi Did the first batch of 2441 diaphragm's from JBL have a dimple in the center and then later change to a small round foil sticker in the center instead of the dimple:hmm: If this is indeed the case how long was the 2441 dia. in use with the dimple before JBL went with the foil sticker and why:hmm:

Any one willing to step forward:hmm: :hmm: :hmm:

I only know the ones with the foil sticker.