There is no chance to label the layout blocks with an offset. If you want to show the previous year, the block has to be labeled with "PY" or similar. To handle it you have to implement a tempcube with the period entity and a capsule procedure which is triggered by screen open trigger like this:
Then you can use the @selection functionalitiy for the block description.
Easier would be the possibility of set the offset manually by adding or subracting month or years like this:
and let the adjustments (necessary offsets) within the layout.