If I have an Excel document that links to other Excel documents and I update
this document which does affect the linked documents, when does that
linking take place? Do all the linked files need to be open when the
initial document is edited or do the linked Excel documents update the next
time they are opened?

All these documents were Excel 2003 format (XLS) and worked fine, since then
they've all been converted to Excel 2007 format (XLSX) and are now
inconsistent in linking.

Any assistance is greatly appreciated.