[Lostgaeriel]

Yes, Merry says in Bree "I have seem them Frodo - Black Riders!". Note that Frodo comes right back at Merry with the same. [Maybe I wasn't clear with the "(...) Black Riders!" I meant that there may or may not be other words before the phrase.]

But Pippin's comment in the house in Crickhollow is a statement, not an exclamation. He says "We were all scared. You would have been, too, if you had been chased for two days by Black Riders."

And of course Frodo asks, as the conspiracy is unmasked, "But what about the Black Riders? Would it be safe to wait one day for Gandalf?"

Check out the meeting with Gildor near Woodhall. "Black Riders!" and "Black Riders?" coming out of everyone's mouths!!!

"(...) Black Riders?" doesn't turn up again until Pippin reaches Minas Tirith.

Considering how omnipresent the Ringwraiths are, it's remarkable how infrequently they are referred to as Black Riders. Or maybe not, since they stop riding horses and start riding those flying creatures.

Your turn, Turambar.