The old data will include timestamps, and those timestamps will be parsed and stored in the system as normal. If the repository is configured with a retention period, and the ingested events are older than the retention period, the ingested data will just be ingested and expired. See Data Retention and Expiration.

Even if the old data is within the retention span, very old data may immediately be offloaded to bucket storage. Querying older data requires this to be loaded back for each executed query.

Ingesting the data, whether or not it's expired, will add additional load to the system and may cause active data for other repositories to be removed from the in-memory cache and slow down their performance.

Be careful if ingesting data into a repository that has alerts or triggers configured. The incoming data may be seen as current (when in fact it is old) and trigger false alerts and notifications.