Not sure if a concatenation or some other formula is neccessary.
Here is what I have:

On 'sheet1'
Column A (A3:A2000) has employee numbers
Column B (B3:B2000) has dates
Column C (C3:C3000) has different codes - this is just text

On 'sheet2'
Row 2 - Cells E2:K2 have dates in them
Column C (C3:C3000) has employee numbers
Column L (L3:L3000)- this is where I need to return the information.

Basically, I'd like to return all of the codes from sheet1 based on the dates only from cells E2:K2 and the employee number on sheet1 and sheet2 (need to match those). I'd like to somehow concatenate all of the codes into the cells in column L, which would only be text.