In another thread the question was raised some time ago whether the Call Number field could be made part of every reference type. The rationale is given in that thread. It seemed like it might be a possibility for the 5.1/6.0 release, but that does not appear to have occurred.

(repeating text from later in that thread, per advice from @adamsmith):

I'm wondering if there are any fields that are visible in ALL ref types, and which could be added as a column to the main view.

Since Call Number is not yet available to all ref types, I am looking for something else that can function as a sort of "call number" of sorts which will hold alphanumerical strings that allow sorting in the main window (I am "call number coding" items using a Luhmann-esque Zettelkasten-type identifier; don't ask).

I had hoped that Loc. in Archive would be such a field (because, well, that is pretty much what the field would be used for), but alas it is not present in Web Page, Blog Post, Email, Podcast, Presentation, etc.

So, is Call Number for all fields far away? And/or is there a field visible in all ref types that could function in its stead (hopefully just in the interim)?