The date carved on this one is the same as the clue... 1668.
5 seconds sound clip from Scooby-Doo, Where Are You! - A Gaggle of Galloping Ghosts (S1E11).
You can hear this line at 00:17:24.252 in the Blu-ray version of the episode.
Quote context
[...]
- A crypt is a tomb where you bury people.
- A tomb?
- Hey, come out from under that sheet!
- OK, Scooby, we'll leave you, but I'd hate to be here alone if those 3 creeps show up.
- We've searched the whole place, and no sign of a clue.
- The date carved on this one is the same as the clue... 1668.
- Shaggy, this stone lid rolls back. Give me a hand.
- If only we could set a trap for that ghoulish ghost.
[...]