(sorry to be so late in getting back w/ more info... my daughter's h.s. b-ball scrimmage had me tied up for most of the evening...)
The marks on my primer were of the type Waywatcher was imagining - where the mark is the same size & shape of the primer rod - where most of the primer was flattened and the crescent shape was the "unflattened crescent on one side.
RCmodel, what you guessed might be Waywtchr's issue is actually mine - small rod w/ the big black insert. Remember the part about being new to this
What a "duh" moment - totally forgot to switch that out.
There is definitely too much wobble w/ the black plastic (large) insert with the small rod.
Here's an odd customer-service related plot twist, though... When I went to assemble the two halves of my smaller white plastic insert, I realized that I have two "left" or "right" halves - not one of each. A little packing error I guess. So, I will in fact be giving RCBS a call about that tomorrow.
When I couldn't try the white insert w/ small rod tonight because of that, I put the black insert back on and used the proper large rod with it. No play or slop at all there. As suspected, since that rod is too large to go "into" the primer pocket of the 9mm, it stops flush w/ the case, leaving the primer where it should be and without any apparent damage/marks.
Great site here. Great folks always willing to help. Thanks for getting me thinking and realizing what the problem was.