You need to carefully read the definition of design characteristics from AS9102
"DESIGN CHARACTERISTICS: Those dimensional, visual, functional, mechanical, and material features or properties, which describe and constitute the design of the article as specified by Drawing Requirements. These characteristics can be measured, inspected, tested, or verified to determine conformance to the design requirements. Dimensional features include in-process locating features such as target-machined (or forged/cast) dimensions on forgings and castings, and, weld/braze joint preparation necessary for acceptance of finished joint. Material features or properties may include processing variables and sequences, which are specified by the drawing (e.g., heat treat temperature, fluorescent penetrant class, ultrasonic scans, sequence of welding and heat treat). These provide assurance of intended characteristics that could not be otherwise defined."
Reference dimensions do not have a tolerance and therefore cannot be measured or confirmed as acceptable. Basic dimensions define a theoretical perfect target and have no tolerance. Their associated GDT reference frames do have tolerance and must be identified and reported. Basic dimensions may or may not be reported as a convienence per specific customer requests.
Basically, if it can be measured or confirmed as acceptable, then it needs to be identified as a required and reported on form 3.
Good luck