Why do some of my 1099-R forms show a State distribution in Box 16 while others leave it blank?

That's a good question.  It really doesn't matter unless there is state tax withheld, in which case the state distribution should be populated.  

Yeah...I'm never quite clear on the why for that.

My two pension 1099-R forms from Fidelity never have the distribution box filled in, even though both have NC taxes withheld.   When I go thru the software though, TTX backfills box 16 with the same value as box 2a  (a valid Box 2a value is defined for both forms).