We are seeing across our various report suites a large delta between total visits and the number of visits that have a referrer type associated with them. Based on the Adobe definition of this dimension I would assume every visit would have a referrer type as the "Typed/Bookmarked" type is intended as a catch all for any visit where adobe does not have any referrer information for it. The deltas we are seeing range from 20% of visits all the way up to 50% of all visits depending on the report suite we are looking at.

Is this common? Is there a particular reason a visit may not have any value here?