Keep author-date multiple year lettering across different documents?

I apologize in advance if this has been answered here, but it’s a somewhat tricky problem. I have a manuscript with many sources of the same author and year in Chicago author-date that I would like to split into separate chapters. This style (and Endnote) applies lettering to those sources with the same author and date (for example, “Smith 2000a” and “Smith 2000b”) succesfully when they are within one document.

My question: is there any way to split up that manuscript’s chapters into separate .docs and maintain that lettering? In other words, if in Chapter 1 I cite Smith 2000a a lot and in Chapter 2 I cite Smith 2000b, is there any way to have these be separate .docs and keep that lettering? Thanks for your advice!

Not without manually changing the Years to include the letter, which isn’t advisable.  You can put the two chapters in different sections – where is the bibliography for the chapters going to end up in the combined book?  - if all together, Endnote will renumber them once they are combined?