I have a SB version D with a totally black mouthpiece, no silver at all on the front. It may be a paint error, but it is factory paint and I thought it may be worth mentioning. Let me know if the pic doesn't work, I'll try to post it again.

Looks like a simple paint error to me.

I have one like that and have seen at least two others besides yours. I agree, it's just a paint error, but somewhat common.

Joebros