Referencing a linked file from INDEX() in Excel (Office 365) - excel

Question

I've got a collection of about 40 Excel worksheets. They store information about the number of hours that people have spent working on different projects, with dates across the top row from left to right and project names down the first column. Each member of the team has their own separate worksheet.
I'm making a new worksheet that will add up the number of hours each person has spent on a specific project.
I'm using this formula to add up all the numbers in a particular range of a linked file:
SUM(INDEX('S:\path\to\folder[Username_2017.xlsx]Daily'!G:JG,JOB_ROW,0))
JOB_ROW is the row containing the numbers I want to add up. Columns G:JG cover 1 Jan - 31 Dec. Username_2017.xlsx is different for each of the 40 people.
The problem is that the formula only works if I create it by hand. I can't find any way to use a dynamic reference to the filename, which gets very tedious with 40+ files to reference. I thought this might work:
SUM(INDEX(INDIRECT(C3),JOB_ROW,0))
...where C3, C4, C5 etc. would contain automatically-generated filenames and references. But it doesn't work. I get #REF!. And Excel doesn't prompt me to link the files -- which suggests to me that it will never work this way.
I've also found that even when the spreadsheet is working properly with the manually-entered formulae, if I save it and re-open it then Excel tries to be helpful by stripping out the formulas and replacing them with the text #REF!.
Is it possible to do what I'm trying to do? Or do I need to learn some VBA?
I should point out that I've largely avoided using Excel in my career so far -- so if there's a better way to achieve this then I'd love to hear it.
Thanks in advance for your help.

Answer 1

ian0411 gave the simple answer to this question in the comments above: the answer is "you can't do that".
If he wants to post that then I'll accept it as an answer -- but for the benefit of anyone else reading this question and looking for alternative options, here's what I tried and what worked:
VBA
I wrote some very simple VBA using GetObject() to open and read from each of the workbooks. It worked, but a) it was very slow, and b) it seemed to keep all the files open as long as Excel was running, which caused other problems. It also crashed a lot.
I gave up on VBA.
Automating the filename replacement
The next option I tried was to have a column of filenames in Excel, with a column next to it containing the formula that I wanted to run on each file. Instead of putting the linked filename in the formula, I put a unique placeholder ('XXXXX' or whatever).
Then I made a little macro that (for the currently selected row) did a search and replace across the row to change 'XXXXX' to the filename in column A. I had to run the macro 40 times to cover each file, but I only had to do that process once. When I add a new file to the list, I'll just add a new line, copy the formulas, and update the filename.
I've now got a spreadsheet which works perfectly when the linked files are closed, and which doesn't rely on VBA.
Perhaps if my VBA skills were better I could have written something less flaky -- but doing it all with INDEX() seems like the fastest, most elegant, and most reliable solution.