I'm a new (reluctant) DM, and my group is currently running through RoT.  We're on chapter 3 and the read aloud text for the Entrance Plaza (p 41) starts, "The entrance to Diderius's Tomb . . ."  Maybe it's just my inexperience as a DM, but I went back and reread the chapter up to that point and I see nowhere that shows when the party is supposed to learn that the place Varram is going to is called the "Tomb of Diderius."  Leosin doesn't mention that name to them, nor does Bolo say it.  The DM-only description doesn't tell me that "everybody knows the Serpent Hills are home to the famous landmark called the Tomb of Diderius."   But suddenly the book is telling me to use that name as if the party is familiar with it. 

Am I thinking too hard about this?  Did I miss something earlier in the chapter that says they learned about the place?

I think it is more of a covert investigation mission. havign read through it there is aparagraph that says

"Harper agents have heard rumors of the theft of the White Dragon Mask, and Leosin Erlanthar has recently learned that the dwarf Varram was seen in the trade settlement of Boareskyr Bridge, near the Serpent Hills. With the Harpers already spread far and wide on their intelligence-gathering missions, the adventurers are a perfect choice to pursue the wyrmspeaker"

So effectively the Harpers send the party to Boareskyr Bridge to see if they can get a lead. So the Harpers are not aware the Tomb is the final destination.

You'd be looking to do Investigation and Persuasion checks at the Inn (although the text does say Bolo is happy to talk about Varram) and then Survival checks to follow him into the serpent hills (again shoul dbe quite easy as its a large group). Sprinkle in some random encounters and then "oh look you find a tomb".

I guess I didn’t phrase my question well.  The characters arrive at “a” tomb, but they don’t know the specific name of the tomb.  However, the read-aloud text has me refer to the tomb’s name as if the group had already discovered its name. I didn’t know if I had overlooked the specific moment where the name should have been revealed to them.

As I said, I’m a newb at DMing.  I grew up playing 3e & 3.5e, now more than a decade later, I’m trying to teach my 8 year old daughter how to play.  With this quarantine going on, we’re progressing through the adventure faster than I can read ahead on it.  So it wouldn’t be out of the realm of possibility that I misread something in my haste.

It does read a bit odd to me as it seems to imply the PC's should know whose tomb it is despite the fact it does say that "Knowledge of the settlement that once stood here
has been lost to all except Ilda, a ghostly librarian in area 9 of the crypt, who has answers to many forgotten questions.", I dont think you've missed anything, its just the way its been written.

I think I would go with an amended decription along the lines of:

"You come across a ruined town  in what was once a large paved plaza. The remains of a fountain are now little more than a stone circle set around a crumbling hole in the ground leading to a well deep below. Two stone statues stand in the courtyard, rising twenty feet high. Behind them, a forty-foot high edifice is carved into the cliff side, dominated by relief columns carved with strange, otherworldly scenes."

then give them the option of searching the cultist camp, maybe throw in a journal or diary entry mentioning the tomb by name or have a grave stone or marker relating to the wizard, then have them approach the statues and eventually find the ghost in are 9 who can dilvulge more info.

That’s a great idea!  I need to get better at altering things on the fly to account for these inconsistencies in the official campaigns.  This isn’t the first such incident of a plot discrepancy I’ve found - it’s just the latest one.

I made my characters give me a Religion/History  check  before mentioning the name of the tomb.