Improve filtering of output webpage

### What problem does your feature request solve?

I can to use an external script to get the same lead time of the same variable for different cases. It would be nice if this level of slicing was available within the GUI.

### Describe the solution you'd like

More slicing!

### Describe alternatives you've considered

Do we need a proper SQL database to back it?

Start by tracing how the GUI generates the output webpage and compare it with the external script that slices lead time for the same variable across cases. Clarify the required slicing options and whether existing data access can support them before deciding if database changes are needed. Done means the GUI provides the requested cross-case slicing behavior.

Written by the indexing model from the issue text.