I'm not sure why, but you are completely missing my point...!
The PZ-109 is not an addition, it is an alternative. Your BL-D200 is (or should be) similar to a PZ-109 with the addition of a right-angled extension for portrait mounting.
As you have acknowledged, the PZ-109 does not fit the D300. So logically, the BL-D200 likewise should not fit a D300. Without an image to demonstrate (you could upload elsewhere and post a link here), I'm afraid I don't understand how you have been able to mount it securely.