Why did you lose 6 months of historical data?
Combination of misconfiguration in polling settings and user error.
Ended up with 6 months of per minute statistics and the database was growing too large. Attempted to change NPM to keep only a week of 1 minute resolution, but the summarization wouldn't complete. I guess it was just too much info to process and summarize. Even trying to incrementally reduce the size didn't work.