Came across this bug the other day and thought I might put it up here so it may help other people. unfortunately I was asked to grab some performance statistics going back to last year. lucky I was running vCOPS which had the data for the dates I needed.
When you select the past year for performance statistics it will only display the last 30 days, this is a bug with vCenter 5.1 GA, A and B and the reference KB is 204264.
There is no fix for this yet but don’t worry the data is still in the DB from what I can see, If you have particularly skilled DBA’s they can modify or fix the procedure or wait for VMware to release a fix.