Vital Status is blank for cases diagnosed in 2015. See "Getting Started" for an explanation about calculating survival for cases diagnosed recently.
Vital Status is the only item for which SEER and CoC agreed to retain different codes to mean the same thing. For historic reasons, SEER uses code 4 for deceased patients while CoC uses 0. All 4s in the CoC database were converted to 0 for the PUF file. There is no Vital Status code for "unknown". Therefore, cases for which the code was not valid are transmitted as blank. They may have been submitted as blanks, 9s, or any other non-defined value. They can be analyzed as "unknown" or omitted from analysis, depending on the needs of the study.