Graph data lost after interruption of service

[farroar]

I am graphing about 50 sources currently. One site went off-line for a few days. After the connection was reset and came back online, data returned to Cacti graphs but no previous data is available from before the outage. Any ideas on why this would happen. In that same time frame, all other sources of data continued to graph fine. It is only this site that is having this issue. I should have a few weeks of data to look at prior to this event but it is all gone now. Does Cacti delete data once an endpoint goes off line for a set amount of time?