VLOOKUP returning wrong values when linked to external sources

It's really weird.  It returns the wrong values but from the correct column (if that makes sense).  For example:  I have the formula written to look for value: PW 123L and return the 2nd column value which should be 123-L but it will return a value of 123-M.  The source workbook data is all correct as I've proofed every row and column value.  In order to correct it all I have to do is click in the formula bar and hit enter and it almost "refreshes" it and returns the correct value.  The only problem with that is these templates I've created are for co-workers to use and these co-workers do not have the level of understanding of Excel that I have so every time they try to use the template they have to contact me to "refresh" the formula in order for the correct data to populate.JKPieterse