Formula only works with referenced workbooks open

First post.

I have a rather involved Summary Workbook with formulas that use INDIRECT() to search individual workbook(s) (and specific worksheets) for data to bring in. Unfortunately, the formula only works if the referenced workbook(s) are open PRIOR TO the Summary Workbook being opened - even when I manually calculate. I would like the Summary Workbook to "find" the data in the other workbooks regardless of them being open or closed.

All workbooks (including the Summary) are stored in the same folder.

I am restricted from using the Trust Center Macro and Update functions due to Group Policy from our network.

Any recommendations would be most appreciated.
Cheers,
robert