We "reuse" published extracts all the time in multiple workbooks. Then you only have to maintain one data source.
Tableau doesn't care what project a data source is published in, BTW. All of our data sources are published in the "Datasources" project, and the workbooks are published in their respective projects.
And yes, I have different published workbooks coming from the same TWB file. Workbook 1 uses dashboard A, B, C and Workbook 2 uses dashboards D, E, F. Each is published under different projects.
Great! Sounds like Tableau "remembers" which workbooks were published with that particular refresh then, even though I scheduled the same Tableau file multiple times.