This is just my Opinion but I have 3 early 69 B body cars and they all have the smaller medallions and my A12 has the larger ones like the 68's. I asked all around when I was redoing my 69 A12 bench seats and Frank B. said all 69's should be the long ones but I know for a Fact that the 1 69 is the Original interior, never changed or used much, and I know the original owner and it has the small ones.

My theory is that in early 69 they started using the small ones but when they sold so many new 69's they ran out of small medallions and started using the 68 medallions to finish the model year with. All the A12 guys have the tall medallions from my research. My satellite hardtop, my satellite conv, and my RR hardtop all have the small one.
Just my 2 cents on this subject.
David