When applying vlookup on lists from different sources, you might easily end up not being able to match values. This guide on Excel help vlookup will show you how to solve common problems on why is vlookup not working such as:
Typical example : SAP extract compared to your local text file, Excel list compared to an SAP extract, Excel list compared to a text list, ...
Using different sources usually is the reason why vlookup in Excel is not working on text, because of different formats used to compare lists in Excel, therefore leading to incorrect results. The solution is to start by putting all your data in a similar format.
See example above. First list as an Excel, second list as a text file. When copying values from text file in Excel, the result is not correct because the Vlookup is applied to compare lists in Excel with different formats:
the value "05678" was present in both lists, but vlookup didn't find it,
the value "19459" was not present in text file, but vlookup did find it.