theoretically exact dimension question

Theoretically Exact Dimensions (TED), also called a "Basic Dimension" should be viewed as dimensions that specify where the tolerance zone is located from which the as-manufactured feature may vary within.

When a TED is specified there should be a geometric tolerance specification somewhere, such as:

Within a note, or table referring to the specific dimension,
Within a tolerance Frame (Feature Control Frame) clearly associated with the feature,
A specified Associated Document or industry standard,
with a general tolerance block specified on the engineering drawing.

Your image came from ASME Y14.5-2009 therefore, See chapter 2, paragraph 2.1.1 "Application".
etc.

When a geometric tolerance is NOT specified, then it can be viewed that the associated feature is established using tooling or gauge tolerances though this interpretation is not always clear.