Nesting Index / Match Function Within Vlookup Function?

let me start by saying that I know an example workbook would be useful here, but the part I'm struggling with is the [managementroster.xlsm] file, and there is A. no way I can release it to the internets and B. its so huge/complicated I couldn't even begin to reproduce a portion of it, scrubbed of data, and hope to maintain its functionality in a meaningful manner.

[Code]....

This formula checks a staff number on this spreadsheet, and then goes and looks at the staff number on the roster. Once found, it returns that staff members roster, but changes any manager codes in the MRC list to Mgr, and changes all other roster codes to Free.

I now need this formula, before altering roster codes to Mgr or Free, to only return codes that are a match for another table (or after really. I don't particularly care, so long as only codes are shown that match data from another table). I think an index/match function would do the trick, but this forumula is already at the edge of my excel ability, nesting another function within it is completey beyond me. The relevant cells for the index/match function would be:

This first Match function targets the column. $E3 is the date required, $BA$1:$DN$1 is the range the dates are entered in
Match: Lookup value = $E3
Lookup array = '[ManagementRoster.xlsm]Vacancies!'$BA$1:$DN$1
match type = 0

This second Match function targets the row. $A$4 is the department name, $B$434:$B$452 is the range where all departments are entered

Match: Lookup value = $A$4
Lookup Array = '[ManagementRoster.xlsm]Vacancies!'$B$434:$B$452
match type = 0

Index: array = $BA$434:$DN$452

So I think my final function is

[Code] .....

But I have absolutely NO idea where it would fit within my first formula, or how to code it so that my original formula only reproduces results that are found in both sheets, or anything.