Hi, Tom.
The term historic flag was not originally included in the Linked.Art version on the Vocabularies, although it has been added to the ULAN JSON-LD after being requested. I can do the same with AAT, if it's important to you to have it in that version of the data. The Linked.Art version of the Vocabularies was intended to be a simplified form of the data, not a complete mapping.
The SKOS (GVP) LOD has the term historic flag, but the value is only explicitly expressed if it is something other than "current." If you look at an instance where the value is something other than "current," you will see it explicitly called out. For example, the "historic" value for the flag is set in the "saturine red" term in the
red lead (pigment) record:
https://vocab.getty.edu/aat/term/1000266748-en
Let me know if you need more information.
Gregg Garcia
Software Architect
Getty Digital, J. Paul Getty Trust