I have multiple sheets in a workbook.

One sheet (call it Sheet A) has data that may or may not be inputted in
specific areas.
Another sheet (call it Sheet B) takes this data and populates cells that are
in Sheet B.

I want some of the data from Sheet A, only if it is has been added, to
populate Sheet B and if it is not populated, I want it to refer to another
cell on Sheet A or to say "not provided".

Is this possible? (or make any sense!)