Andi,
You could put a simple formula into column c2 and copy down to C1709
=countif(B:B,A2)
This would return a 1 for every claim that has been paid, with the added bonus that it would return greater than 1 if the claim has been paid more than once (Assuming that these are one off claims and you should only be paying them once!)
You could also place conditional formatting into the claim cell, to highlight those that have been paid/not paid.
But I'm sure a Guru will post a much better method soon.
Daz