CountBLANK not working with Vlookup function

I have 3 worksheets for 3 separate managers, each sheet has a column which uses a COUNTBLANK function to work out the number of days off an employee has had off in the last two weeks:

Now the formula works perfectly on each worksheet, however I also have a master worksheet (which is identically set out and formatted to the 3 manager sheets) which uses a vlookup formula to pull the data from all 3 worksheets into one at the beginning of the workbook.

The problem I've come across is that the COUNTBLANK formula doesn't work on the master worksheet - I think this has something to do with the vlookup formula entered into the cells which I consider to be blank, but excel doesn't?

I've tried using a separate vlookup formula to pull the data from the 3 managers worksheets and this does work unless an employee appears on more than one managers' sheet - then the data from both worksheets is added together.....

Is there another function I could use to display the information I need to?

Thanks in Advance