If someone had later stage cancers would a CBC blood test be normal?

Possibly. Honestly, it would depend on the specific cancer and where and if it has spread to other sites. For instance, melanoma would likely have a normal count but leukemia would not.
A CBC may. Be completely normal with very advanced cancer - - it measures red cells and their parameters, white cells, number and type, and platelets...Some include a differential that reports type and per cent of white cells. Some advanced cancers may cause problems, more from treatment, but a CBC is not a monitor for cancer stage, prognosis or expectations of any kind.