Currently it seems to be impossible to create a custom rolling date range that stays relative to the Panel Date Range when that range has a variable number of days (eg. when panel date range has fixed start and rolling end, or when users change the panel date range). Without this, you cannot create standard comparison periods such as 'Same period previous year'), meaning you have to create a custom rolling range for every new project, and even then, if the user changes the panel date range to something with a different number of days, the custom range gets out of alignment.
The easiest way to fix this is to allow custom date ranges to reference the Panel End Date as well as the Panel Start Date. eg. a 'Same Period previous year' date range could be defined as...
Start Date = Panel Start Date -365
End Date = Panel End Date - 365
