as I understand it, the default behaviour of baselining in SQL Monitor is that you have access to any part of a rolling window of the most recent 28 days and that metrics can be averaged into regions. My concern is that with this approach recent comes to mean the same thing as normal - exceptional or deteriorating performance gets absorbed into the averaged baseline regions. What used to be normal - the original baseline - will get purged according to the SQL Monitor purge configuration.
Is there a way, either through standard SQL Monitor functionality or with a (simple?) script against the monitoring database, to capture a few weeks of baseline data long term (and have this available as a baseline within SQL Monitor)? In this way it would be possible to compare current performance with that of a year ago (say), without having to store a full 12 months of metrics.