Language survived, partially.

Ceremony survived, partially, underground and in the memory of individuals who maintained it despite official suppression.

Oral tradition survived, selectively.

Whether the specific knowledge of Crazy Horse’s burial location survived this period — in the form of complete location information, or as fragmentary accounts, or as the general knowledge that the location is protected but not its specific coordinates — is not established.

The disruption of the boarding school era is one of the factors that makes it plausible that specific pieces of knowledge were lost.