Multiple References in same cell

Hi All,

I'm wondering if this is at all possible.

Attached is the workbook I need help with. On the 'Pre work' sheet, I have Names, Performance Scores & Potential Scores. I have concatenated the performance scores and the potential scores in Column A in order for me to use the Vlookup function to pull the data through in the Fill sheet.

The problem I have is that this only pulls through 1 reference, where I need all applicable references. In the Fill sheet, the cells are black where there should be more than one reference, and in the Pre work sheet, the cells are highlighted that have more than one person meeting the criteria.

I have tried the following array formula, but it takes FOREVER!:

{=INDEX('Pre work'!A:B,SMALL(IF('Pre work'!A:A=F1&A18,ROW(A:A)),ROW(1:1)),2)}

I then concetenated a second and third, etc formula in this same cell, manually adjusting the ROW(1:1) portion each time...

I am looking for a solution that will give me multiple references in the same cell, that I will not have to manually copy and paste formulas and concatenate them, and that will also not be extremely taxing on the processors. It took about 10 seconds to do 1 cell, as I have 400+ entries.

Please can somebody help.