The current description of Application.calculate indicates this:
"Recalculate all currently opened workbooks in Excel".
But on my tests (through an addin and in ScriptLab) it does only recalculate the active workbook, which seems coherent with the current status of APIs not allowing to "play" with other workbooks (there's no WorkbookCollection class, for instance).
Is this an error on the description?
Or should I expect recalculation on workbooks other than the active one?
PS: on this StackOverflow post from 5 years ago, one of yours specified this which would confirm my thoughts:
"It shouldn't trigger this across workbooks however, only the workbook held by this application instance."